Engineering Commons^™

Engineering Order-Disorder Transitions For High-Performance Thermoelectric Fe2val Heusler Alloys, Cory T. Cline

Dartmouth College Ph.D Dissertations

Fe₂VAl shows great promise as an eco-friendly and low-cost replacement to conventional low-temperature (250-500 K) thermoelectric materials. Current thermoelectric materials use toxic and expensive elements like Te and Sb, whereas Fe₂VAl offers a larger power factor at a lower cost and a reduced risk of environmental pollution. The key issue with Fe₂VAl is the alloy’s relatively large thermal conductivity compared to its semiconductor competitors. This thesis aims to investigate a hierarchical approach to reduce lattice thermal conductivity through a preliminary exploration of heavy element substitutions and mechanical deformation, then through probing order-disorder transitions for …

Characterization Of Materials Properties In Additively Manufactured Aisi-420 Martensitic Steel Deposited By Laser Engineered Net Shaping, Md Mehadi Hassan

Nanoscience and Microsystems ETDs

Metal additive manufacturing (AM) is a disruptive technology enabling the fabrication of complex and near-net-shaped parts by adding material layer-wise. It offers reduced lead production time. AM processes are finding applications in many industrial sectors such as aerospace, automotive, biomedical, and mold tooling. Despite the tremendous advantages of AM, some challenges still prevent this technology's adoption in high-standard applications. Anisotropy and inhomogeneity in the mechanical properties of the as-built parts and the existence of pores and lack-of-fusion defects are considered the main issues in directed energy deposition (L-DED) parts. Laser-engineered net shaping LENS® offers excellent possibilities to fabricate metal tools …

Methodologies For Improvement Of Metal Fatigue Life, Ali Haghshenas

LSU Doctoral Dissertations

A methodology is proposed to identify the onset of crack initiation that utilizes the material damping. The damping is measured using the impulse excitation technique (IET). The damping is also used to correlate fatigue life of additively manufactured (AM) specimens to their damping characteristics. Results reveal that the damping value is inversely proportional to the fatigue life of the specimens.

To detect the damage accumulation and crack initiation in metals due to cyclic loading, another methodology based on the measurement of the surface roughness parameters is introduced. Results presented reveal that the evolution of the surface roughness parameters can be …

The Influence Of Heat Treatment On Corrosion Behavior Of Martensitic Stainless Steel Uns 42670, Armen Kvryan

Boise State University Theses and Dissertations

Ceaseless demand for lighter, faster, and more efficient aircraft has been one of the greatest driving forces behind bearing steel innovations. Recent studies demonstrate that corrosion is one of the leading causes of bearing failure in both military and commercial aircraft. High-performing bearing steels are available but are not being used in US military applications due to high cost and security issues when steels are produced outside of the continental United States. One approach to address this issue is to engineer steels that are cost-efficient and heat treated for corrosion resistance, long wear life, etc.

This dissertation presents information on …

A Study Of The Effect Of Heat Treatment On 3d Printed Pla Impact Strength, Suresh Thota

Electronic Theses and Dissertations

Environmental conditions have a significant effect on the mechanical properties of various materials. Environmental parameters such as temperature and humidity have a major impact on mechanical properties of materials such as compressive strength, tensile strength, bending strength and impact strength. The purpose of this research is to study how temperature and humidity affect the impact strength of 3D printed PLA plastic. Impact strength is the ability of a material to absorb energy subjected to an impact load by a pendulum. In this research, 3D printing was employed to produce PLA specimens which were later used for different experimental testings. For …

The Effects Of Atmospheric Heat Treatments On Tio2 Nanotube Anodes For Lithium-Ion Batteries, Andreas Savva

Boise State University Theses and Dissertations

The effects of various heat treatments on the physical and electrochemical properties of anatase TiO₂ nanotubes were studied in this work. Well-ordered TiO₂ nanotubes were grown via electrochemical anodization and annealed at 450°C to induce a phase transformation to anatase. The heat treatments were conducted under atmospheres of O₂, Ar, N₂, and water vapor (WV) to create different point defects. The oxygen-deficient atmospheres were used to generate oxygen vacancies in the TiO₂ nanotubes, while the water vapor treatment was used to create Ti vacancies by stabilizing them via the protonation of O sites. …

Material-Process-Property Relationships Of 17-4 Stainless Steel Fabricated By Laser-Powder Bed Fusion Followed By Hot Isostatic Pressing., Harish Irrinki

Electronic Theses and Dissertations

17-4 PH stainless steel is commonly used in medical, tooling, automotive, chemical and aerospace industries due to its excellent strength and corrosion properties. Additive manufacturing processes such as laser-powder bed fusion (L-PBF) have gained attention and importance due to the potential to produce complex-shaped three-dimensional parts for various industries. In order to manufacture three-dimensional components from 17-4 PH stainless steel powder using L-PBF, it is critical for design and manufacturing engineers to have an awareness of various material options and corresponding processing and post-processing conditions to obtain useful mechanical properties from the process. The goal of this dissertation is to …

Effect Of Thermal Treatment On High Temperature Deformation Of Alloy Ep-~823, Martin Milburn Lewis

UNLV Theses, Dissertations, Professional Papers, and Capstones

The objective of this research topic is to determine mechanical properties of Alloy EP-823 and to provide a mechanistic understanding of its sensitivity to both thermal treatment and performance temperature. EP-823 is a leading target material for accelerator-driven waste transmutation applications. Overall, the tensile test results of Alloy EP-823 indicated a general trend of decreasing mechanical performance with an increase in tempering time. An increase in tempering time had a statistically significant inverse relationship with ultimate tensile strength (UTS) and yield strength (YS). An increase in tempering time did not have a significant effect on elongation and reduction in area. …

Effect Of Heat Treatment On The Mechanical Properties In Natural Bamboo, Austin Levy, Mackenzie Kirkpatrick

Materials Engineering

Previous studies have shown that heat treatments have the ability to improve mechanical strength and stiffness in hardwood species. Compared to structural hardwoods, bamboo is a more sustainable and globally viable renewable resource. Therefore, Bambusoides vivax (timber bamboo) culms were fabricated into flat, rectangular cross-section samples with varying cellulose content to be heat treated and tested for mechanical properties. All samples were heat treated (HT) twice. The first HT was a normalization of all samples at 103 +/- 3 °C. The second HT was performed at various times and temperatures ranging from 130°C to 170°C for 0.5 to 3 hours. …

Microstructure And Chemistry Evaluation Of Direct Metal Laser Sintered 15-5 Ph Stainless Steel, Kevin Coffy

Electronic Theses and Dissertations

15-5PH stainless steel is an important alloy in the aerospace, chemical, and nuclear industries for its high strength and corrosion resistance at high temperature. Thus, this material is a good candidate for processing development in the direct metal laser sintering (DMLS) branch of additive manufacturing. The chemistry and microstructure of this alloy processed via DMLS was compared to its conventionally cast counterpart through various heat treatments as part of a characterization effort. The investigation utilized optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-Ray diffractometry (XRD), energy dispersive X-Ray spectroscopy (EDS) and glow discharge atomic emission spectrometry (GDS) …

The Effects Of Heat Treatment On Area Percent Porosity And Corrosion Behavior Of High-Nickel Thermal Spray Coatings, Travis Crowe, Alec Guraydin

Materials Engineering

Samples of two Thermal Spray Coating (TSC) alloys on a low carbon steel substrate were obtained: alloy C276 and Nicko-Shield 200. Specimens of each alloy were subjected to heat treatments at temperatures at 1100° for 60 minutes and 1200° for 10 minutes, with some specimens left in the as-sprayed condition. Three replicates were prepared for each condition. Thin 1” strips were cut using a diamond wafering blade for porosity measurements and 2” x 1” specimens were cut for corrosion testing using a SiC abrasive saw. The porosity specimens were mounted in acrylic resin, polished, and examined using SEM. From these …

Characterization Of The Relationship Between The Microstructure And Tensile Strength Of Annealed Ti-6al-4v, Aldo Corona

Materials Engineering

Tensile coupons of Ti-6Al-4V were heat treated at varying annealing temperatures from 1200°F (648°C) to 1450°F (787°C) at 50°F (23°C) increments for 1 hour. The samples were air cooled to room temperature or furnace cooled to 800°F (426°C) followed by air cooling to room temperature. Four tensile coupons were treated at each annealing temperature and cooling rate. Alpha case was observed to form on the surface of the samples post heat treatment with a maximum depth of 25 µm (.001 in). Samples were tensile tested for their ultimate tensile strength, yield strength, and percent elongation. Samples across all annealing temperatures …