Browsing by Subject "microhardness"

Now showing 1 - 6 of 6

Effects of Heat Treatment and Fast Neutron Irradiation on the Microstructure and Microhardness of Inconel 625 Fabricated via Laser-Powder Bed Fusion
(University of Texas at Austin, 2021) Keya, T.; O'Donnell, V.; Lieben, J.; Romans, A.; Harvill, G.; Andurkar, M.; Gahl, J.; Thompson, S.M.; Prorok, B.C.
The microstructure of Inconel 625 fabricated via Laser-Powder Bed Fusion (L-PBF) was investigated in as-printed and heat-treated conditions. The very high cooling rates inherent to the L-PBF process generally result in fine microstructures and complex residual stress fields which requires annealing to reduce stress and tailor the microstructure to obtain the desired mechanical properties. Inconel 625 alloy, a nickel-based superalloy, continues to be a common material employed with the L-PBF process. The unique microstructure produced by the L-PBF process and different phases introduced by different heat treatment processes require investigation to facilitate the material’s wide range of applications. This paper investigates the influence of heat treatments at 700°C, 900°C and 1050°C for one hour on the microstructure and microhardness of the L-PBF parts. The parts were irradiated using ‘fast’ neutrons in University of Missouri Research Reactor Center (MURR). The microhardness before and after radiation are also compared.
Mechanical Performance of Selective Laser Melted 17-4 PH Stainless Steel Under Compressive Loading
(University of Texas at Austin, 2017) Ponnusamy, P.; Masood, S.H.; Ruan, D.; Palanisamy, S.; Rahman Rashid, R.A.; Ahmed Mohamed, Omar
Selective Laser Melting (SLM) is a powder-bed type Additive Manufacturing (AM) process, where metal powder melting is followed by rapid solidification to yield metallic components. The mechanical performance of the components is greatly influenced by various SLM process parameters such as laser power, scan speed, scan pattern, hatch distance, build orientation, layer thickness and defocus distance. Studies on compressive properties of stainless steel parts by SLM have received relatively little attention. In this study, an investigation was conducted to assess the influence of laser power, build orientation, layer thickness and laser defocus distance on the mechanical behaviour of selective laser melted 17-4 PH stainless steel parts under quasi-static compression. Fractional factorial design was used to optimise the four process parameters to obtain maximum hardness and compressive strength with least porosity. Results are supported by studies on porosity and microstructure observations.
Microstructural and Mechanical Performance of Al2O3 Nanoparticle Reinforced 17-4 PH Stainless Steel Bulk Composite Parts Fabricated by Laser Engineered Net Shaping Process
(University of Texas at Austin, 2016) Ning, Fuda; Hu, Yingbin; Liu, Zhichao; Wang, Hui; Cong, Weilong; Li, Yuzhou
Alloy 17-4 PH (AISI 630) is a precipitation-hardening martensitic stainless steel that has been extensively employed in the industries of aerospace, marine, and chemical. In this study, bulk parts of both 17-4 PH and Al2O3 reinforced 17-4 PH composites were fabricated on a steel substrate by laser engineered net shaping (LENS) process to investigate the effects of Al2O3 reinforcements on the part performance. The 17-4 PH powders were pre-mixed with Al2O3 nanoparticles by ball milling. The microstructures of both parts were observed using scanning electron microscopy and mechanical properties including microhardness and compressive properties were evaluated by means of a Vickers microhardness tester and a universal tester, respectively. The results indicate that Al2O3 reinforced 17-4 PH composite parts fabricated by LENS process exhibited superior microhardness and compressive properties as compared to pure 17-4 PH parts.
Microstructure and Mechanical Behavior of AlCoCuFeNi High-Entropy Alloy Fabricated by Selective Laser Melting
(University of Texas at Austin, 2017) Zhang, M.N.; Zhou, X.L.; Zhu, W.Z.; Li, J.H.
Additive manufacturing (AM) technique, such as selective laser melting (SLM) is a modern method for materials fabrication and formation. In this study, AlCoCuFeNi HEA parts are fabricated by SLM using prealloyed powders prepared by atomization process. The effect of processing parameters on microstructures, microhardness and compression property of SLM-fabricated HEA parts are systematically investigated. Results show that input laser energy density involved in laser power and scan speed plays a significant role in the densification behavior. A near-full 99.03% density is achieved as an energy density of 102.5 J/mm3 . The alloys consist of simple body-centred cubic (BCC) structure and exhibit the highest microhardness up to 541.17 HV0.2 and compressive strength of 1621.1 MPa due to the BCC solid solution strengthening. The study reveals that SLM is advantageous to produce the high-entropy alloy with high density, good mechanical properties and even complicated shapes.
Processing and Characterization of 3D-Printed Polymer Matrix Composites Reinforced with Discontinuous Fibers
(University of Texas at Austin, 2019) Gupta, Ankit; Hasanov, Seymur; Fidan, Ismail
The objective of this study is to fabricate discontinuous fiber (short fiber) reinforced polymer matrix composite material (CM) by additive manufacturing (AM) technology using single extruder 3D printer. For this study, short carbon fibers (diameter = 7.2μm, length = 150μm) reinforced filaments were extruded with fiber concentrations of 3% - 7.5% in volume. Input process parameters used for 3D printing to obtain good quality short carbon fiber (SCF) reinforced polymer specimens are reinforcement percentage and printing speed by fixing nozzle temperature, layer thickness, bed temperature and print orientation. It was analyzed that the surface characteristics and mechanical performance of 3D printed samples are greatly influenced by varying input process parameters. Scanning electron microscopy was performed to observe microstructural behavior of 3D printed samples. Tensile strength, ductility, and toughness were examined to validate the adhesiveness of the matrix and reinforcement. From the microhardness test, it was observed that the hardness properties are significantly affected by increasing the reinforcement percentage. The results obtained in this study could be quite useful in fabricating polymer matrix composites (PMCs) with improved overall characteristics for applications in automotive industry and medical field.
Residual Stress Measurements via X-ray Diffraction Cos α Method on Various Heat-Treated Inconel 625 Specimens Fabricated via Laser-Powder Bed Fusion
(University of Texas at Austin, 2021) Andurkar, Mohanish; Suzuki, Toshikazu; Omori, Masanao; Prorok, Bart; Gahl, John; Thompson, Scott
The residual stress and hardness of Inconel 625 fabricated using Laser Powder Bed Fusion (L-PBF) were experimentally investigated. As-built Inconel 625 samples were subjected to three different heat-treatment temperatures of 700℃, 900℃, 1050℃ for one hour. Effects of these three-stress relieving heat treatment temperatures on the nature and value of residual stress were studied. Residual stress measurements were recorded using a portable X-ray system. The system calculated residual stress using the cos α method. The Full Width Half Maximum (FWHM) of diffraction peaks in all samples were measured. The results indicate that tensile residual stress was present on the surface of as-built L-PBF sample and compressive residual stress on the surface of heat-treated samples due to stress relief. Debye-Scherrer (D-S) ring positions were measured using the cos α method and compared with a reference wrought Inconel 625 ring position. Vickers microhardness and residual stress were found to be positively correlated.