Metallurgy Commons^™

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 …

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 …

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.

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. …

Functionally Graded Materials By Laser Metal Deposition (Preprint), Syamala R. Pulugurtha, Joseph William Newkirk, Frank W. Liou, Hsin-Nan Chou

Materials Science and Engineering Faculty Research & Creative Works

Fabrication of functionally graded materials (FGMs) by laser metal deposition (LMD) has the potential to offer solutions to key engineering problems over the traditional metalworking techniques. But the issues that need to be addressed while building FGMs are intermixing in the layers and cracking due to the residual stresses. This paper is to present the study of the effect of process parameters (laser power and travel speed) on the degree of dilution between the substrate (or, previous layer) and powder material for few metallurgical systems.

Effect Of Friction Stir Processing On Fatigue Behavior Of An Investment Cast Al-7si-0.6 Mg Alloy, S. Jana, Rajiv S. Mishra, J. B. Baumann, G. Grant

Materials Science and Engineering Faculty Research & Creative Works

Cast aluminum alloys in general show poor fatigue performance due to the presence of defects. Friction stir processing (FSP) can be used as a tool to enhance the mechanical properties of cast alloys by eliminating such defects. in the present study FSP led to a five times improvement in fatigue life of an investment cast Al-7Si-0.6 Mg hypoeutectic alloy. the reason for such an enhancement was linked to the closure of casting porosities, which acted as crack nucleation sites in the as cast condition. Porosities acted as notches in the as cast alloy and led to an order of magnitude …

Controlling Strength And Permeability Of Silica Investment Casting Molds, Darryl M. Kline

Masters Theses

"Investment casting is a metal casting process in which a ceramic mold is created around a disposable pattern using dip coating. The fine silica flour making up most of the mold gives the benefits of a smooth internal mold surface and high density. The high density allows for investment casting molds to be thinner and lighter than sand-based molds, but gives substantially smaller gaps between particles for air flow. This research focused on the design and improvement of the formulation for making investment casting molds with customizable physical properties. Properties of the molds, specifically flexural strength, permeability, and physical structure, …

Foundry Parameters For Casting High-Aluminum Lightweight Steel In Complex Shapes, Angella Marie Schulte

Masters Theses

"This work investigated the liquid metal treatment and molding practices for Fe- 30wt.%Mn-9wt.%Al-1wt.%Si-0.9wt.%C-0.5wt.%Mo steel. The goal of this research was to determine the process conditions that would produce a tough Fe-Mn-Al-C alloy and the appropriate mold design to produce a defect-free P900 plate.

Notch toughness of age-hardenable Fe-Mn-Al-C alloys decreases as phosphorus increases. Thermodynamic calculations and experimental work show that additions of Ca followed by Ce can be used to mitigate the deleterious effects of phosphorus, and the addition of Ar-stirring can be used to decrease the number of harmful aluminum nitride inclusions. In the solution-treated and aged condition (Brinell …

Evaluation Of Alternative Methods For Surface Preparation And Deposition Of Cerium-Based Conversion Coatings On Aluminum Alloys, William J. Gammill

Masters Theses

"This thesis investigates alternative surface preparation and deposition methods for cerium-based conversion coatings (CeCC) on high strength aluminum alloys. Cerium-based conversion coatings are being investigated as a more environmentally friendly replacement for chromium-based conversion coatings. Currently, the alloys are immersed in strong alkaline and acidic solutions to prepare the aluminum surfaces for conversion coating, in which immersion may not be suitable for all situations. Alternatives to this method were investigated, including wipe application of solution, ultrasonic processing in deionized water, and abrasive blasting with alumina. AI 7075-T6 test panels were prepared using each of these methods and compared to a …

Influence Of Fraction Of High Angle Boundaries On The Mechanical Behavior Of An Ultrafine Grained Al-Mg Alloy, R. Kapoor, N. Kumar, R. S. Mishra, C. S. Huskamp, K. K. Sankaran

Materials Science and Engineering Faculty Research & Creative Works

The mechanical behavior of ultrafine grained AA5052 processed through different techniques-rolled, annealed, friction stir processed (FSP) and equal channel angular pressed (ECAP)-were compared and correlated with microstructure. the microstructure was characterized using electron back scattered diffraction to obtain the boundary spacing, the fraction of high angle boundaries and to estimate the dislocation density from local misorientations. Both FSP and ECAP conditions had ultrafine boundary spacing, but the fraction of high angle boundaries was larger for the FSP condition. Tensile deformation carried out at 297K, and 10-3s-1 showed a lower work-hardening rate and recovery rate for FSP as compared to the …

Friction Stir Processing Of Commercial Grade Marine Alloys To Enable Superplastic Forming, Christopher B. Smith, Arun Mohan, Rajiv S. Mishra, Murray Mahoney, Mike Miles, Scott M. Gillis, Lee M. Cerveny, Gerald Opichka

Materials Science and Engineering Faculty Research & Creative Works

The use of friction stir processing (FSP) on marine grade aluminum sheet has been investigated with the objective of locally enhancing the material properties. This can potentially allow low-cost commercial grade aluminum to be used in superplastic forming applications or further enhance the formability to allow more complex geometries to be formed. FSP has been demonstrated to enable super plasticity (uniform elongations >250%) in 5083-H116 over a range of friction stir processing conditions. © (2010) Trans Tech Publications.

An Analysis Of Strength And Ductility Of Ultrafine Grained Al Alloys, R. Kapoor, P. S. De, R. S. Mishra

Materials Science and Engineering Faculty Research & Creative Works

This paper brings together and compares data of various ultrafine grained (UFG) Al alloys processed through different routes. in general, the trend of decreasing ductility with increasing strength was observed for the UFG alloys. as compared to the coarse grained (CG) alloys, the UFG alloys show a lower ductility, a lower extent of work-hardening and a lower uniform elongation. Unlike the CG alloys, which show a large fraction of uniform to total elongation, in UFG alloys this fraction varies with processing technique. It is shown here that aging of some UFG Al alloys improves ductility. Further, it is shown that …

Factors Controlling Ductility In Ultrafine Grain Aluminum Alloys Under Monotonic And Cyclic Loading, Partha Sarathi De

Doctoral Dissertations

"Ultrafine grained (UFG) Al processed by severe plastic deformation (SPD) methods are characterized by high strength and a limited uniform ductility. Friction stir processing (FSP), an offshoot of friction stir welding has emerged as a new technique to produce UFG alloys. FSP-UFG Al alloys show a distinctly different behavior with higher uniform elongation and improved high cycle fatigue life as compared to other SPD processed variants. The objective of this work was to study the microstructural basis for such mechanical behavior in FSP-UFG Al alloys.

To study the mechanical behavior of FSP Al alloys, a subsize bending fatigue and uniaxial …

Characterization Of Diamond Thin Films And Related Materials, Travis K. Mckindra

Doctoral Dissertations

"Thin carbon films including sputtered deposited graphite and CO₂ laser-assisted combustion-flame deposited graphite and diamond thin films were characterized using optical and electron microscopy, X-ray diffraction and micro-Raman spectroscopy. Amorphous carbon thin films were deposited by DC magnetron sputtering using Ar/O₂ gases. The film morphology changed with the oxygen content. The deposition rate decreased as the amount of oxygen increased due to oxygen reacting with the growing film. The use of oxygen in the working gas enhanced the crystalline nature of the films. Graphite was deposited on WC substrates by a CO₂ laser-assisted O₂/C₂H₂ combustion-flame method. Two distinct microstructural areas …

Dependency Of Machinability In Gray Cast Iron On Nitride-Induced Age Strengthening, Jared Teague

Doctoral Dissertations

"Work of previous researchers has suggested that room temperature age strengthening in gray cast irons improves machinability. Verification and quantification of the machinability improvement is important to industry. Improved machinability will reduce overall manufacturing costs and reduce raw material consumption by decreasing the rate at which tools are replaced. Experimental work was performed to determine a connection between improved machinability in gray cast iron and changes in machining mechanics. An industrial tool wear study verified that age strengthening improved machinability by reducing tool wear to less than one-quarter of the unaged value. Laboratory tests on iron castings from the same …

Understanding Corrosion Of Ni₃(Si,Nb) Alloys In Hot Sulfuric Acid, Jen-Hsien Hsu

Doctoral Dissertations

"The Sulfur-Iodine thermochemical cycle has been proposed as a method for producing large quantities of hydrogen gas from water. However, the extreme operating environments involved limit the possible materials for construction.

Through proper heat treatment and composition control, the modified patented Ni₃(Si,Nb) alloy keeps high temperature strength to greater than 750⁰C and can be deformed by cold rolling more than 50% using multiple passes and intermediate anneals. The corrosion resistance is reproducible and maintains less than 5 mpy for a broad range of boiling sulfuric acid concentrations, including 70 wt%.

In the boiling 70 wt% sulfuric acid corrosion tests, kinetic …

Fluid Flow Related Phenomena And Inclusion Motion In Continuous Casting Strands, Yufeng Wang

Doctoral Dissertations

"To improve the efficiency of the continuous casting process and the quality of its products, this dissertation mainly investigated fluid flow related phenomena and inclusion motion in continuous casting. Mathematical simulation was performed for this purpose. Both a slab caster and a billet caster were investigated. In the study of the slab caster, the application of electromagnetic brake field on the slab mold was evaluated. The results indicated that the magnetic force decelerated the high speed steel jet, stabilized the top fluctuation, and prevented the bias flow inside the mold. The other study of this slab caster involved the fluid …

Effect Of Stress Ratio On The Fatigue Behavior Of A Friction Stir Processed Cast Al-Si-Mg Alloy, S. Jana, Rajiv S. Mishra, J. B. Baumann, G. Grant

Materials Science and Engineering Faculty Research & Creative Works

The effect of friction stirs processing (FSP) on the fatigue life of a cast Al-7Si-0.6 Mg alloy at stress ratios of R = 0 and R = -1 was evaluated. Two types of specimen geometry were used for the FSPed condition, through thickness processed and partial thickness processed. at R = 0, the microstructural refinement enhanced the fatigue life by a factor of 15, whereas at R = -1 the improvement in fatigue life was 5-fold. in light of these observations, various closure mechanisms were examined. © 2009 Acta Materialia Inc.

Increase Of Heat Transfer To Reduce Build Time In Rapid Freeze Prototyping, Ming-Chuan Leu, Sriram Praneeth Isanaka, Von Richards

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Reduction of part build time in the Rapid Freeze Prototyping (RFP) process, which fabricates a 3D ice part layer-by-layer by depositing and freezing water droplets, has been achieved by increase of heat transfer. Three mechanisms have been experimentally investigated: 1) cooling the substrate, 2) use of forced convection, and 3) use of a chilling plate. Cooling the substrate is effective for parts of small heights but becomes ineffective with increase in part height. Forced convection produced desirable reduction in part build time but with the undesirable formation of frost on the built ice part. The use of chilling plate to …

Dislocation-Particle Interaction At Elevated Temperatures, Rajiv S. Mishra

Materials Science and Engineering Faculty Research & Creative Works

There is a major difference in dislocation-particle interaction at low and elevated temperatures. This article will only discuss the historic development of and the current understanding of the interaction of dislocations with non-shearable particles at elevated temperatures. It will show that the understanding of repulsive-attractive transition in dislocation-particle interaction at elevated temperatures has undergone remarkable change and is at a level where a physics-Based high-temperature strengthening framework can be developed. © TMS 2009.

Fatigue Of Friction Stir Welded Lap Joints With Sealants, Kenneth Doering

Masters Theses

"A lack of understanding of corrosion fatigue in friction stir welded aluminum joints prevents friction stir welding from being implemented in aerospace applications. Fatigue testing reveals a 60-75% reduction in the fatigue life of friction stir welded aluminum lap joints immersed in 3.5% NaCl solution (corrosion fatigue) compared with that of lap joints tested in ambient air. The loss in fatigue life is attributed to accelerated fatigue cracking due to hydrogen environment embrittlement. Two polymer sealant candidates are investigated: silicone rubber and nylon-11. Both sealant candidates can be applied prior to welding and seal the faying surface gaps in lap …

The Effect Of Near-Surface Metallurgy On The Machinability Of Cast Iron, William Dewey Peach

Masters Theses

"The increasing performance and durability of cutting tool inserts have created metallurgical challenges for production foundries to produce near-net shaped castings within strict dimensional tolerances. In order for foundries to take full advantage of the increased cutting speed capabilities, it becomes necessary to reduce machining allowances and produce much more stable casting surfaces. To accomplish this, a better understanding of the complex microstructures formed within the first 0.120 in. (3 mm) of the mold/metal interface (as-cast surface) is necessary. The goal of the work presented here was to examine the microstructures formed in the near-surface region of gray iron castings, …

Microstructural Influence On Dynamic Properties Of Age Hardenable Femnal Alloys, Ryan A. Howell

Doctoral Dissertations

"A lightweight castable alloy was sought to reduce the MIL-PRF-32269 class II cast steel perforated armor's weight with the requirement that the material had to be manufactured utilizing existing foundry technology and without incurring large alloy cost increases to meet property requirements. Literature on wrought age hardenable Fe-Mn-Al-C alloys suggested this alloy system could achieve weight reduction through high aluminum concentrations with the highest reported strengths exceeding 2 GPa for a Fe-30Mn-9Al-0.9C composition. Even though ballistic testing had not been conducted on this system, high strain rate data of wrought alloys showed excellent work hardenability; greater than existing ballistic metals. …

Material Flow And Microstructure Evolution In Friction Stir Welding Of Aa6111 Alloy Sheets, Manasij Kumar Yadava

Doctoral Dissertations

"Material flow and microstructure evolution are the two important aspects of the Friction stir welding (FSW) technique, which control the properties and performance of the friction stir welds. The present work investigates these two aspects of the FSW with main emphasis on the friction stir lap joints (FSLJs) on the AA6111 sheets. Due to the characteristic material flow during FSW, the faying surfaces in FSLPs are deposited in and around the weld nugget and create unavoidable defects. These defects reduce the load carrying thickness of the joints by providing an easy path for the weld failure. Therefore, to control the …

The Role Of Friction Stir Processing On The Microstructure And Mechanical Properties Of A Cast Aluminum Alloy, Saumyadeep Jana

Doctoral Dissertations

"Al-7Si-0.6Mg is one of the most important cast aluminum alloys because of its attractive mechanical properties and high castability. Microstructurally, the alloy consists of primary aluminum dendrites with eutectic Si particles in the interdendritic region. This makes the alloy quasi-brittle in nature which affects the ductility of the alloy to a great extent. In order to improve the ductility, the eutectic Si particles need to be refined which so far has been achieved by chemical and/or thermal modification. Friction stir processing (FSP) on the other hand can achieve the same through plastic deformation, and therefore replace the cast structure with …

Thermal Characterization And Vibration Of Solder Alloys, Brandon Lee Brinkmeyer

Masters Theses

"Recent legislation and growing environmental concerns have forced the electronics industry to discontinue the use of tin-lead (SnPb) solder. Although the legislation did not directly affect aerospace and defense industries, future transitions to lead-free (LF) solders are inevitable. Differences exist between these high reliability systems and consumer electronics, first of which is a very small production rate and a long life cycle which often leads to repair or rework procedures which introduce the potential for mixing of SnPb and LF solder. In this study, Sn-3Ag-0.5Cu (SAC305) was mixed with Sn-37Pb solder in amounts of 0, 25, 50, 75, and 100 …

Elevated Temperature Behavior Of A Magnesium Based Bulk Metallic Glass, Neal C. Ross

Masters Theses

"Bulk metallic glasses are a new material set that possess interesting and exceptional engineering properties. Their study has been a major focus of research in metallurgy since the early 1990s, and recently their properties have led to application in specialized applications. Limitations including material cost, maximum attainable cast diameters, and high density have prevented the widespread use of these materials. In particular, the high density of most bulk metallic glasses has significantly reduced their appeal to the aerospace community. In an effort to overcome this, research is being performed on producing lower density glass forming systems based on magnesium and …

Thickness Effects On The Ac And Dc Electrical Behavior Of Rf-Sputtered Batio3 Nano-Capacitors With Pt And Ni Electrodes, James N. Reck, Matthew O'Keefe, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Nanoscale BaTiO₃ capacitors were deposited on Si wafers at dielectric thicknesses of approximately 25, 50, 100, and 200 nm using RF-magnetron sputtering with either 25 nm thick Ni or Pt electrodes. Multiple DC and AC tests were conducted on these devices to determine the effects of BaTiO₃ thickness on the measured dielectric behaviors. All films were observed to have non-linear responses for resistance, permittivity, and loss with respect to dielectric thickness. The permittivity was found to follow a standard dead layer model behavior with measured values ranging from approximately 350 to 1700 for Ni electrodes and approximately 100 …

Geological Sequestration Of Carbon Dioxide By Hydrous Carbonate Formation In Steelmaking Slag, C. Hank Rawlins

Doctoral Dissertations

"The formation of carbonate solids from the alkaline earth oxide phases in steelmaking slag was investigated in dry and aqueous conditions as a vehicle for carbon dioxide sequestration. The goal of this research was to determine the process conditions that would increase the kinetics of the carbonate formation process under hydrous conditions, enabling direct removal of carbon dioxide from steelmaking offgas"--Abstract, page iv.

Preface, Judy Schneider, Rajiv S. Mishra, Thomas R. Bieler, Yuntian T. Zhu, Khaled B. Morsi, Viola L. Acoff, Eric M. Taleff, Ruslan Valiev

Materials Science and Engineering Faculty Research & Creative Works

No abstract provided.