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Materials Science and Engineering Faculty Research & Creative Works

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Microstructural Evolution And Mechanical Properties Of Friction Stir Welded Ods Alloy Ma754, Jiye Wang, Wei Yuan, Rajiv S. Mishra, Indrajit Charit Sep 2013

Microstructural Evolution And Mechanical Properties Of Friction Stir Welded Ods Alloy Ma754, Jiye Wang, Wei Yuan, Rajiv S. Mishra, Indrajit Charit

Materials Science and Engineering Faculty Research & Creative Works

Microstructural evolution and mechanical properties of MA754, an yttrium oxide dispersion-strengthened nickel-based superalloy, were investigated after friction stir welding (FSW). A tool rotation rate of 1000 revolution per minute and a traverse speed of 50.8 mm per minute were employed using a cermet (WC-Co) tool. After FSW, fine equiaxed grain structure with a high dislocation density and a random texture was achieved. Agglomeration of yttrium oxide dispersoids was observed in FSW MA754. Room-temperature tensile properties of FSW MA754 were compared to those of as-received MA754 alloy, and the results indicated that particle strengthening contribution decreased as a result of dispersoid …

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Additivity Of Strengthening Mechanisms In Ultrafine Grained Al-Mg-Sc Alloy, N. Kumar, R. S. Mishra Sep 2013

Additivity Of Strengthening Mechanisms In Ultrafine Grained Al-Mg-Sc Alloy, N. Kumar, R. S. Mishra

Materials Science and Engineering Faculty Research & Creative Works

In the light of unique and anomalous properties of ultrafine grained (UFG) alloys, an effort was made to develop a predictive capability of the yield strength (YS) of UFG Al-Mg-Sc alloy. UFG microstructure was introduced using friction stir processing. Microstructural characterization of grain size, dislocations, and nano-sized Al3(Sc,Zr) particles was carried out using electron backscatter diffraction and transmission electron microscope. The contribution from Peierls-Nabarro stress, solid solution strengthening, precipitation strengthening, grain boundary strengthening, and dislocation strengthening were assessed using existing strengthening models. Additivity law to predict the YS of the alloy was chosen based on the microstructural state of the …

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Effect Of Zinc Galvanization On The Microstructure And Fracture Behavior Of Low And Medium Carbon Structural Steels, Ignatius C. Okafor, Ronald J. O'Malley, Kaushal R. Prayakarao, Heshmat A. Aglan Aug 2013

Effect Of Zinc Galvanization On The Microstructure And Fracture Behavior Of Low And Medium Carbon Structural Steels, Ignatius C. Okafor, Ronald J. O'Malley, Kaushal R. Prayakarao, Heshmat A. Aglan

Materials Science and Engineering Faculty Research & Creative Works

Microstructure and fracture behavior of ASTM 572 Grade 65 steels used for wind tower applications have been studied. Steels of two carbon level chemistries designed for this grade were used in the study. Fracture toughness of the steels was studied using 3-point bend test on samples coated with zinc and not coated with zinc. Lower carbon steel showed higher resistance to fracture than medium carbon steel after zinc galvanization. SEM study suggests that zinc and zinc bath additives that migrated to crack tips are responsible for the loss in ductility. The phenomenon of Liquid Metal Embrittlement (LME) is suggested to …

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Achieving High Strength And High Ductility In Friction Stir-Processed Cast Magnesium Alloy, Wei Yuan, Sushanta K. Panigrahi, Rajiv S. Mishra Aug 2013

Achieving High Strength And High Ductility In Friction Stir-Processed Cast Magnesium Alloy, Wei Yuan, Sushanta K. Panigrahi, Rajiv S. Mishra

Materials Science and Engineering Faculty Research & Creative Works

Friction stir processing (FSP) is emerging as an effective tool for microstructural modification and property enhancement. As-cast AZ91 magnesium alloy was friction stir processed with one-pass and two-pass to examine the influence of processing conditions on microstructural evolution and corresponding mechanical properties. Grain refinement accompanied with development of strong basal texture was observed for both processing conditions. Ultrafine-grained (UFG) AZ91 was achieved under two-pass FSP with fine precipitates distributed on the grain boundary. The processed UFG AZ91 exhibited a high tensile strength of ∼435 MPa (117 pct improvement) and tensile fracture elongation of ∼23 pct. The promising combination of strength …

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Influence Of Strain And Strain Rate On Microstructural Evolution During Superplasticity Of Mg-Al-Zn Sheet, A. Mohan, S. K. Panigrahi, R. S. Mishra, R. Verma Aug 2013

Influence Of Strain And Strain Rate On Microstructural Evolution During Superplasticity Of Mg-Al-Zn Sheet, A. Mohan, S. K. Panigrahi, R. S. Mishra, R. Verma

Materials Science and Engineering Faculty Research & Creative Works

Strain-induced abnormal grain growth was observed along the gage length during high-temperature uniaxial tensile testing of rolled Mg-Al-Zn (AZ31) sheet. Effective strain and strain rates in biaxial forming of AZ31 sheets also affected the nature of grain growth in the formed sheet. For the uniaxial testing done at 400 C and a strain rate of 10-1 s-1, abnormal grain growth was prevalent in the gage sections that experienced true strain values between 0.2 and 1.0. Biaxial forming of AZ31 at 5 x 10 -2 s-1 and 400 C also exhibited abnormal grain growth at the cross …

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Microstructure And Mechanical Properties Of A Friction Stir Processed Ti-6al-4v Alloy, Jianqing Su, Jiye Wang, Rajiv S. Mishra, Ray Xu, John A. Baumann Jun 2013

Microstructure And Mechanical Properties Of A Friction Stir Processed Ti-6al-4v Alloy, Jianqing Su, Jiye Wang, Rajiv S. Mishra, Ray Xu, John A. Baumann

Materials Science and Engineering Faculty Research & Creative Works

Friction stir processing (FSP) trials were performed on 2mm-thick Ti-6Al-4V sheets using various processing parameters including tool rotational speed (800-1000RPM) and tool traverse speed (1-4IPM). A processing window was established with the W-1% La2O3 tool to produce defect-free friction stir processed (FSP'd) materials. The stir zone (SZ) material of the FSP'd samples showed a fully Β transformed microstructure characterized by typical basket-weave lamellar α/Β structure. The prior Β grains in the SZs contained multiple α variants, and the average sizes ranged from 12μm to 38μm influenced by the processing parameters. Based on metallurgical evaluation, the microstructural evolution …

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Superplasticity And Microstructural Stability In A Mg Alloy Processed By Hot Rolling And Friction Stir Processing, V. Jain, R. S. Mishra, R. Verma, E. Essadiqi Apr 2013

Superplasticity And Microstructural Stability In A Mg Alloy Processed By Hot Rolling And Friction Stir Processing, V. Jain, R. S. Mishra, R. Verma, E. Essadiqi

Materials Science and Engineering Faculty Research & Creative Works

The superplastic behavior of a Mg-1.2 Zn-1.7 Y-0.53 Al-0.27 Mn alloy sheet processed by hot rolling and friction stir processing (FSP) was investigated. The kinetics of superplastic deformation were compared with Mg-3 Al-1 Zn and other Mg-Zn-Y alloys processed by different methods. The FSP Mg-1.2 Zn-1.7 Y-0.53 Al-0.27 Mn alloy exhibits slower kinetics of deformation compared with other alloys. The microstructural stability of the FSP Mg-1.2 Zn-1.7 Y-0.53 Al-0.27 Mn alloy is better than the Mg-3 Al-1 Zn alloy because of the presence of different types of precipitates. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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Stress Corrosion Cracking Susceptibility Of Ultrafine Grained Al-Mg-Sc Alloy, G. R. Argade, N. Kumar, R. S. Mishra Mar 2013

Stress Corrosion Cracking Susceptibility Of Ultrafine Grained Al-Mg-Sc Alloy, G. R. Argade, N. Kumar, R. S. Mishra

Materials Science and Engineering Faculty Research & Creative Works

General corrosion and stress corrosion cracking (SCC) behavior of coarse grained, fine grained and ultrafine grained (UFG) AA5083 and Al-Mg-Sc-Zr alloy in different thermomechanical conditions were studied in the present work. Friction stir processing (FSP) was carried out to refine the grain size. The average grain size achieved after FSP for AA5083 was 7±3μm, whereas that for Al-4Mg-0.8Sc-0.08Zr was 0.39±0.16μm with 100% UFG microstructure. Linear polarization resistance and cyclic polarization techniques were used to study general corrosion behavior of these alloys in 3.5wt% NaCl solution. The UFG microstructure showed the highest polarization resistance (Rp) of ~93kΩ which increased to ~160kΩ …

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High Strain Rate Superplasticity In Friction Stir Processed Ultrafine Grained Mg-Al-Zn Alloys, A. Mohan, W. Yuan, R. S. Mishra Feb 2013

High Strain Rate Superplasticity In Friction Stir Processed Ultrafine Grained Mg-Al-Zn Alloys, A. Mohan, W. Yuan, R. S. Mishra

Materials Science and Engineering Faculty Research & Creative Works

Friction stirs processing of a rolled AZ31 alloy, and a high pressure die cast AZ91 alloy produced ultrafine grained materials with average grain size of 0.8μm and 0.5μm, respectively. Tensile testing was done in the temperature range of 210-360°C and strain rate range of 1x10-4-3x10-2s-1. Higher amounts of Β-precipitates in AZ91 thermally stabilized the microstructure up to 330°C. Friction processed ultrafine grain AZ91 exhibited high strain rate super plasticity at all tested temperatures. The best elongation of 1251% was achieved at a strain rate of 1x10-2s-1 and temperature of 330°C. The …

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Effect Of Friction Stir Processing On The Tensile And Fatigue Behavior Of A Cast A206 Alloy, R. Kapoor, K. Kandasamy, R. S. Mishra, J. A. Baumann, G. Grant Jan 2013

Effect Of Friction Stir Processing On The Tensile And Fatigue Behavior Of A Cast A206 Alloy, R. Kapoor, K. Kandasamy, R. S. Mishra, J. A. Baumann, G. Grant

Materials Science and Engineering Faculty Research & Creative Works

The microstructure of cast Al alloy A206 was modified using friction stir processing (FSP) to eliminate porosity, break down intermetallic particles and refine the grains. The inference from differential scanning calorimetry is that the nugget region of the as-FSP material contained primarily GP zones. Uniaxial tensile tests and bending fatigue tests were carried out at room temperature on A206 alloy in the cast and T4 conditions and after FSP with different heat treatments - as-FSP, FSP and aging, and FSP with solutionizing and aging. These produced varied microstructures with combinations of pores, grain sizes, precipitate types and particle sizes. The …

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Effect Of Inhomogeneous Deformation On Anisotropy Of Az31 Magnesium Sheet, Jidong Kang, David S. Wilkinson, Raja K. Mishra, Wei Yuan, Rajiv S. Mishra Jan 2013

Effect Of Inhomogeneous Deformation On Anisotropy Of Az31 Magnesium Sheet, Jidong Kang, David S. Wilkinson, Raja K. Mishra, Wei Yuan, Rajiv S. Mishra

Materials Science and Engineering Faculty Research & Creative Works

Inhomogeneous plastic deformation in AZ31 magnesium sheet has been studied during uniaxial tensile testing using digital image correlation and electron backscatter diffraction techniques. Large strain gradients develop on the sheet surface parallel and perpendicular to the loading direction while very little deformation occurs in the thickness direction. This lack of thinning leads to an abrupt fracture following the development of a premature but extensive diffuse neck but without any localized neck. The strain distribution on the sheet surface evolves nonlinearly with strain, impacting the measured plastic strain ratio, r-value. The results show that r-value should be measured at "points" rather …

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Microstructure And Mechanical Properties Of Friction Stir Welded Oxide Dispersion Strengthened Alloy, Jiye Wang, Wei Yuan, Rajiv S. Mishra, Indrajit Charit Jan 2013

Microstructure And Mechanical Properties Of Friction Stir Welded Oxide Dispersion Strengthened Alloy, Jiye Wang, Wei Yuan, Rajiv S. Mishra, Indrajit Charit

Materials Science and Engineering Faculty Research & Creative Works

Effect of friction stir welding (FSW) on microstructure and mechanical properties of oxide dispersion strengthened alloy MA956 was investigated. Fine grained microstructure was developed in the processed region with slight particle coarsening. Tensile behavior of the processed material was compared with that of the as-received material at room temperature. Results indicated that significant grain refinement during FSW compensated for the reduced particle strengthening contribution and enhanced tensile strength by 145 MPa without loss in ductility. Further analysis indicated a good agreement between experimentally measured yield strength and the strength calculated by Pythagorean superimposition of strengthening contribution in FSWed material. © …

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Grain Size And Texture Effects On Deformation Behavior Of Az31 Magnesium Alloy, W. Yuan, R. S. Mishra Dec 2012

Grain Size And Texture Effects On Deformation Behavior Of Az31 Magnesium Alloy, W. Yuan, R. S. Mishra

Materials Science and Engineering Faculty Research & Creative Works

Cold rolled AZ31 magnesium alloy sheet was subjected to friction stir processing to generate four average grain sizes ranging from 0.8 to 9.6 μm. the processed material exhibited a strong basal fiber texture with the c-axis tilted about 35-55° towards the processing direction. the grain size and texture dependence of mechanical behavior were evaluated by using tensile testing along two orthogonal directions. Remarkably high ductility of ~65% was achieved in relatively coarse-grained material that fractured without developing necking when tested in the processing direction. the ductility decreased significantly to ~10% for ultrafine grained material as the tensile yield strength increased …

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A Comparative Study On The Corrosion Resistance Of Cerium-Based Conversion Coatings On Az91d And Az31b Magnesium Alloys, C. E. Castano, Surender Maddela, Matthew J. O'Keefe, Y. M. Wang Dec 2012

A Comparative Study On The Corrosion Resistance Of Cerium-Based Conversion Coatings On Az91d And Az31b Magnesium Alloys, C. E. Castano, Surender Maddela, Matthew J. O'Keefe, Y. M. Wang

Materials Science and Engineering Faculty Research & Creative Works

In the present work a comparative study has been carried out on the surface morphology, electrochemical properties and corrosion performance of cerium-Based conversion coatings (CeCCs) on AZ91D and AZ31B magnesium alloys. the as-deposited coatings consisted of a two-layer structure: A continuous Mg/Al oxide transition layer of ∼ 50 nm thick and a CeCC layer of ∼ 400 nm thick. Potentiodynamic polarization and impedance spectroscopy results using a 0.6 wt.% NaCl and 0.6 wt.% (NH4)2SO4 electrolyte showed that cerium-Based conversion coatings enhanced the corrosion resistance of AZ91D and AZ31B magnesium alloys compared to polished uncoated samples. …

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Stress Corrosion Cracking Susceptibility Of Ultrafine Grained Az31, G. R. Argade, W. Yuan, K. Kandasamy, R. S. Mishra Oct 2012

Stress Corrosion Cracking Susceptibility Of Ultrafine Grained Az31, G. R. Argade, W. Yuan, K. Kandasamy, R. S. Mishra

Materials Science and Engineering Faculty Research & Creative Works

In this study, stress corrosion cracking (SCC) behavior of AZ31 magnesium alloy was carried out using slow strain rate testing (SSRT) technique in 3.5 wt.% NaCl solution. the influence of microstructural scale on the stress corrosion behavior was investigated in AZ31 alloy with three different mean grain sizes. Single-pass and two-pass friction stir processing (FSP) was employed to obtain fine grain and ultrafine grain microstructures, respectively. for FSP, SSRT specimens were extracted from the processed region. SSRTs were carried out in air and solution at an initial strain rate of 10 -6/s. a significant decrease in the ultimate tensile strength …

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Transition Of Deformation Behavior In An Ultrafine Grained Magnesium Alloy, S. K. Panigrahi, K. Kumar, N. Kumar, W. Yuan, R. S. Mishra, R. Delorme, B. Davis, R. A. Howell, K. Cho Jul 2012

Transition Of Deformation Behavior In An Ultrafine Grained Magnesium Alloy, S. K. Panigrahi, K. Kumar, N. Kumar, W. Yuan, R. S. Mishra, R. Delorme, B. Davis, R. A. Howell, K. Cho

Materials Science and Engineering Faculty Research & Creative Works

The deformation behavior of friction stirs processed magnesium alloy with average grain size ranging from 25 μm to 240 nm was studied. an evaluation of critical grain size for transition of deformation mode from twinning to slip was carried out by employing tensile and compressive tests. the role of critical grain size in transition of deformation behavior from strain hardening to softening was established. Inhomogeneous yielding was observed during tensile test of ultrafine-grained magnesium alloy below the critical grain size. © 2012 Elsevier B.V.

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Process Optimization For Friction-Stir-Welded Martensitic Steel, M. Ghosh, K. Kumar, R. S. Mishra Jun 2012

Process Optimization For Friction-Stir-Welded Martensitic Steel, M. Ghosh, K. Kumar, R. S. Mishra

Materials Science and Engineering Faculty Research & Creative Works

Advanced high-strength M190 steel sheets were joined by friction-stir welding under different tool rotational and traversing speeds. the optical microstructure of the joints exhibited complete martensite and partial martensite at the weld nugget depending on the cooling rate during welding. the first heat-affected zone outside of the weld nugget revealed ferrite-pearlite phase aggregate, and the second heat-affected zone showed a tempered martensitic structure. the interplay of process variables in terms of peak temperature and cooling rate was studied to observe their effect on joint efficiency under shear testing. the peak hardness at weld nugget was close to the parent alloy …

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Material Flow And Microstructural Evolution During Friction Stir Spot Welding Of Az31 Magnesium Alloy, W. Yuan, Rajiv S. Mishra, B. Carlson, R. Verma, R. K. Mishra May 2012

Material Flow And Microstructural Evolution During Friction Stir Spot Welding Of Az31 Magnesium Alloy, W. Yuan, Rajiv S. Mishra, B. Carlson, R. Verma, R. K. Mishra

Materials Science and Engineering Faculty Research & Creative Works

Material flow and local texture evolution during friction stir spot welding (FSSW) of AZ31 magnesium alloy was characterized by varying tool rotation rates. Texture at various locations of the welded region was measured using electron backscatter diffraction (EBSD). Material flow is significantly influenced by tool rotation rate with a conical step spiral pin tool, and FSSW introduces a unique basal fiber texture in the welded region. Results indicate that local texture evolution is dominated by shear deformation through material flow. the tool shoulder applies both shear and compressive deformation to the upper region material; however, the rotating pin introduces only …

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Hot Deformation Behavior Of Friction-Stir Processed Strip-Cast 5083 Aluminum Alloys With Different Mn Contents, M. A. García-Bernal, Rajiv S. Mishra, R. Verma, D. Hernández-Silva Feb 2012

Hot Deformation Behavior Of Friction-Stir Processed Strip-Cast 5083 Aluminum Alloys With Different Mn Contents, M. A. García-Bernal, Rajiv S. Mishra, R. Verma, D. Hernández-Silva

Materials Science and Engineering Faculty Research & Creative Works

Fine grained 5083 aluminum alloy is the most common Al-Mg alloy for superplastic forming (SPF) of lightweight sheet metal parts in the automotive and aerospace industries. the fine-grained sheet is industrially produced by massive cold rolling of conventionally rolled sheet stock at high cost. Friction stir processing (FSP) as a thermomechanical process is very effective in refining the microstructure of as-cast alloys such as that produced by continuous strip casting (CC). in this work, the effect of friction stirs processing on the superplastic properties of three CC 5083 aluminum alloys, with different Mn content, has been investigated. the three alloys …

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Directional Anisotropy In The Mechanical Behavior Of Friction Stir Processed And Aged Az91 Alloy, Vipin Jain, Wei Yuan, R. S. Mishra, Gouthama, Anil K. Gupta Jan 2012

Directional Anisotropy In The Mechanical Behavior Of Friction Stir Processed And Aged Az91 Alloy, Vipin Jain, Wei Yuan, R. S. Mishra, Gouthama, Anil K. Gupta

Materials Science and Engineering Faculty Research & Creative Works

Friction stir processing (FSP) is an emerging grain refinement technique for magnesium alloys. in this study, a cast AZ91 alloy was processed by a single-pass FSP to achieve an average grain size of ∼6 μm in the nugget zone. the FSP is found to introduce texture in the alloy due to preferred alignment of basal poles in the processing direction. the mechanical behavior is significantly influenced by texture. after FSP, the alloy was aged at different temperatures and times for continuous and discontinuous precipitation of β-Mg17Al12. a high anisotropy in yield stress is observed in the processing and transverse direction …

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Influence Of Grain Size And Texture On Hall-Petch Relationship For A Magnesium Alloy, W. Yuan, S. K. Panigrahi, J. Q. Su, R. S. Mishra Dec 2011

Influence Of Grain Size And Texture On Hall-Petch Relationship For A Magnesium Alloy, W. Yuan, S. K. Panigrahi, J. Q. Su, R. S. Mishra

Materials Science and Engineering Faculty Research & Creative Works

Friction stir processing was applied to a magnesium alloy to generate various grain sizes with the same intense basal texture. Subsequent tensile deformation along two orthogonal directions by easy activation or inhibition of basal slip follows the Hall-Petch relationship between yield stress and grain size in both directions. the Hall-Petch parameters are texture dependent. Easy activation of basal slip introduces lower values, while inhibition of basal slip leads to higher values. the Hall-Petch parameters are interpreted by texture and microstructural factors. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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Grain Boundary Behavior In An Ultrafine-Grained Aluminum Alloy, P. S. De, R. S. Mishra Dec 2011

Grain Boundary Behavior In An Ultrafine-Grained Aluminum Alloy, P. S. De, R. S. Mishra

Materials Science and Engineering Faculty Research & Creative Works

The low-angle grain boundary (LAGB) stability in an ultrafine-grained (UFG) Al alloy during monotonic loading was investigated by orientation imaging microscopy (OIM). the experiments show that boundaries with misorientation below ∼2.5 deg are stable, while boundaries with misorientation between 2.5 and 15 deg are unstable. Similar results were observed during cyclic loading of UFG Al alloy. This behavior was rationalized using the nonequilibrium thermodynamics concept. on the other hand, it is postulated that the grain boundary behavior in microcrystalline alloy is different because of the larger dislocation mean free path. © 2011 the Minerals, Metals & Materials Society and ASM …

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A Study On The Combined Effect Of Forging And Aging In Mg-Y-Re Alloy, S. K. Panigrahi, W. Yuan, R. S. Mishra, R. Delorme, B. Davis, R. A. Howell, K. Cho Jan 2011

A Study On The Combined Effect Of Forging And Aging In Mg-Y-Re Alloy, S. K. Panigrahi, W. Yuan, R. S. Mishra, R. Delorme, B. Davis, R. A. Howell, K. Cho

Materials Science and Engineering Faculty Research & Creative Works

The combined effect of forging and aging on microstructural evolution and mechanical properties of a Mg-Y-RE alloy was studied in the present work by employing hardness measurements, tensile tests, optical microscopy (OM), scanning electron microscopy (SEM) and electron back scattered diffraction (EBSD) analysis. the -F temper treated bulk Mg-Y-RE alloy samples were subjected to forging for microstructural refinement and subsequent aging to maximize the strength-ductility combination. the forged samples combined with peak aging treatment (60 h at 180 °C) exhibited an excellent combination of high strength (388 MPa) and high ductility (23%). the combined effect of grain refinement, work hardening, …

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A Stress-Strain Model For A Two-Phase Ultrafine-Grained Aluminum Alloy, P. S. De, J. Q. Su, R. S. Mishra Jan 2011

A Stress-Strain Model For A Two-Phase Ultrafine-Grained Aluminum Alloy, P. S. De, J. Q. Su, R. S. Mishra

Materials Science and Engineering Faculty Research & Creative Works

Two-phase ultrafine-grained (UFG) aluminum alloys with different precipitate and low-angle boundary distributions were examined for their monotonic stress-strain behavior. Precipitates in combination with low-angle grain boundaries were found to determine the deformation micro mechanism. It is proposed that thermally activated vacancy movement plays a central role in this regard. the experimental stress-strain curves matched well with the trend predicted by a modified Blum-Zheng model based on vacancy-assisted dislocation annihilation mechanism. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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Friction Stir Lap Welded Advanced High Strength Steels: Microstructure And Mechanical Properties, M. Ghosh, K. Kumar, R. S. Mishra Jan 2011

Friction Stir Lap Welded Advanced High Strength Steels: Microstructure And Mechanical Properties, M. Ghosh, K. Kumar, R. S. Mishra

Materials Science and Engineering Faculty Research & Creative Works

Friction stir welding was carried out under different heat input and cooling rates to produce lap joints between high strength martensitic steel sheets. the microstructure of the welds was characterized, and microhardness was evaluated. Joint efficiency was determined by lap shear test. Variation in processing conditions governed total heat input, peak temperature and cooling rate during friction stir welding. Weld nugget microstructure depended principally on cooling rate. the slowest cooling rate promoted ferrite-pearlite and the fastest cooling rate resulted in martensite formation in the weld nugget. the weakest region of all the joints was the heat affected zone, which consists …

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Effect Of Process Parameters On Abnormal Grain Growth During Friction Stir Processing Of A Cast Al Alloy, S. Jana, Rajiv S. Mishra, J. A. Baumann, G. Grant Nov 2010

Effect Of Process Parameters On Abnormal Grain Growth During Friction Stir Processing Of A Cast Al Alloy, S. Jana, Rajiv S. Mishra, J. A. Baumann, G. Grant

Materials Science and Engineering Faculty Research & Creative Works

The effects of process parameters and friction stir processing (FSP) run configurations on the stability of nugget microstructure at elevated temperatures were evaluated. Cast plates of an Al-7Si-0.6Mg alloy were friction stir processed using a combination of tool rotation rates and tool traverse speeds. All single pass runs showed some extent of abnormal grain growth (AGG), whereas multi-pass runs were more resistant to AGG. Additionally, higher tool rotation rate was found to be beneficial for controlling AGG. These effects were analyzed by comparing the result of this work with other published results and AGG models. © 2010 Elsevier B.V.

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Microstructural Evolution During Fatigue Of Ultrafine Grained Aluminum Alloy, P. S. De, Rajiv S. Mishra Nov 2010

Microstructural Evolution During Fatigue Of Ultrafine Grained Aluminum Alloy, P. S. De, Rajiv S. Mishra

Materials Science and Engineering Faculty Research & Creative Works

A comparative study of the surface microstructural changes during fatigue of a precipitation hardened (PH) aluminum alloy in ultrafine grained (UFG) and microcrystalline conditions was done using orientation imaging microscopy (OIM). with increase in applied stress amplitude, the fatigue life of fine-grained PH alloy deteriorated. on the other hand, at lower stress amplitudes an improvement in fatigue life was noted. This trend was reversed for the coarse-grained PH alloy. in UFG alloy, the fatigue life improved at all stress amplitudes. the variation in fatigue life response between coarse, fine and ultrafine grain PH alloy was due to the increased interaction …

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Effect Of Friction Stir Processing On Microstructure And Tensile Properties Of An Investment Cast Al-7si-0.6mg Alloy, Saumyadeep Jana, Rajiv S. Mishra, John A. Baumann, Glenn J. Grant Oct 2010

Effect Of Friction Stir Processing On Microstructure And Tensile Properties Of An Investment Cast Al-7si-0.6mg Alloy, Saumyadeep Jana, Rajiv S. Mishra, John A. Baumann, Glenn J. Grant

Materials Science and Engineering Faculty Research & Creative Works

Friction stir processing (FSP) is emerging as a promising tool for microstructural modification. the current study assesses the effects of FSP on the microstructure and mechanical properties of an investment cast Al-7Si-Mg alloy. FSP eliminates porosity and significantly refines eutectic Si particles. the extent of particle refinement varied with changes in processing conditions. a high tool rotation rate and a low-to-intermediate tool traverse speed generated a higher volume fraction of finer particles. Tensile ductility changed significantly as a result of FSP, whereas ultimate tensile strength improved only marginally. Yield strength was similar in both cast and FSP samples under various …

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Analysis Of Microstructural Evolution During Friction Stir Welding Of Ultrahigh-Strength Steel, M. Ghosh, K. Kumar, R. S. Mishra Oct 2010

Analysis Of Microstructural Evolution During Friction Stir Welding Of Ultrahigh-Strength Steel, M. Ghosh, K. Kumar, R. S. Mishra

Materials Science and Engineering Faculty Research & Creative Works

Friction stirs lap-welded advanced high-strength M190 steel exhibited formation of lath martensite at weld nuggets, a ferrite layer at faying surfaces and a ferrite-pearlite microstructure at the bottom of the stir zone. the phase transformation was governed by severe plastic deformation in the austenitic region followed by cooling. the strain rate and peak temperature played key roles in controlling the prior-austenitic grain size and were correlated to the Zener-Hollomon parameter. an empirical relationship has been obtained for dynamically recrystallized austenite grains. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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Investigation Of Creep Threshold Stresses Using In Situ Tem Straining Experiment In An Al-5y2o3-10sic Composite, S. P. Deshmukh, Rajiv S. Mishra, I. M. Robertson Apr 2010

Investigation Of Creep Threshold Stresses Using In Situ Tem Straining Experiment In An Al-5y2o3-10sic Composite, S. P. Deshmukh, Rajiv S. Mishra, I. M. Robertson

Materials Science and Engineering Faculty Research & Creative Works

Creep behavior of metal matrix composites is similar to dispersion strengthen alloys and characterized by the presence of a threshold stress below which the creep rate is negligible. This threshold stress is attributed, at least in dispersion-strengthened alloys, to dislocation particle interactions in which the detachment of the dislocations from the particle is the rate-limiting step. Creep experiments were performed on an Al-5Y2O3-10SiC composite in the temperature range of 473 and 573 K and the nature of the dislocation-particle interaction was determined by performing in situ straining experiments at elevated temperature in a transmission electron microscope. …

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