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Microstructure-Properties Relationships of Ti-6Al-4V Parts Fabricated by Selective Laser Melting
Justin Mezzetta,Joon-Phil Choi,Jason Milligan,Jason Danovitch,Nejib Chekir,Alexandre Bois-Brochu,Yaoyao Fiona Zhao,Mathieu Brochu 한국정밀공학회 2018 International Journal of Precision Engineering and Vol.5 No.5
This work investigates the relationships between the static mechanical properties of Ti-6Al-4V manufactured through selective laser melting (SLM) and post-process heat treatments, namely stress relieve, annealing and hot isostatic pressing (HIP). In particular, Ti-6Al-4V parts were fabricated in three different build orientations of X, Z, and 45o to investigate the multi-directional mechanical properties. The results showed that fully densified Ti-6Al-4V parts with densities of up to 99.5% were obtained with optimized SLM parameters. The microstructure of stress relieved and mill annealed samples was dominated by fine α′ martensitic needles. After HIP treatment, the martensite structure was fully transformed into α and β phases (α+β lamellar). Within the realm of tensile properties, the yield and ultimate strength values were found statistically similar with respect to the built orientation for a given heat treatment. However, the ductility was found orientation dependent for the HIP samples, where a lower value was observed for samples built in the X direction.
Hamid Javadi,Walid Jomaa,Victor Songmene,Myriam Brochu,Philippe Bocher 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.8
An original approach is introduced to discriminate the effects of residual stress and surface roughness on turned Inconel 718 alloy parts. This could be used for assessing or studying the performance of these specimens during fatigue tests. This method consists of building surface integrity maps in terms of surface roughness parameters and residual stress in order to select specific turning conditions with adequate machining parameters. The surface integrity maps were generated by using response surface methodology based empirical models and precision turning tests on coupons. The proposed approach was therefore successfully applied to manufacture rotating bending fatigue specimens with the surface axial residual stress varying from − 239 to 446 MPa while keeping the arithmetic average roughness and the surface hoop residual stress constant. The effect of the surface axial residual stress on the fatigue life could thus be discriminated from the other surface integrity characteristics effects. The proposed methodology is independent of the manufacturing process and can be extended to other machining processes such as milling, grinding, and broaching.
Choi, Joon-Phil,Shin, Gi-Hun,Brochu, Mathieu,Kim, Yong-Jin,Yang, Sang-Sun,Kim, Kyung-Tae,Yang, Dong-Yeol,Lee, Chang-Woo,Yu, Ji-Hun JAPAN INSTITUTE OF METALS 2016 MATERIALS TRANSACTIONS Vol.57 No.11
<P>Selective laser melting (SLM) is an attractive manufacturing technique for the production of metal parts with complex geometries and high performance. This manufacturing process is characterized by highly localized laser energy inputs during short interaction times which significantly affect the densification process. In this present work, experimental investigation of fabricating 316L stainless steel parts by SLM process was conducted to determine the effect of different laser energy densities on the densification behavior and resultant microstructural development. It was found that using a low laser energy density below 50 J/mm(3) produced an instable melt pool that resulted in the formation of unmelted particles, pores, cracks, and balling in the as-built parts with low densification. In contrast, the as-built parts at a high energy density above 200 J/mm(3) showed irregular scan tracks with a number of pores and metal balls that decreased part density. The optimal laser energy density range was accordingly determined to be 58-200 J/mm(3) by eliminating obvious SLM defects, which led to near full densification. The SLM samples fabricated using optimal parameters allowed observation of a microhardness of 280 Hv, ultimate strength of 570 MPa, and yield strength of 530 MPa that were higher than those of the as-cast and wrought 316L stainless steel.</P>
Choi, J.P.,Shin, G.H.,Yang, S.,Yang, D.Y.,Lee, J.S.,Brochu, M.,Yu, J.H. Elsevier Sequoia 2017 Powder technology Vol.310 No.-
<P>In this study, the densification behavior and microstructural development of Inconel 718 parts fabricated by selective laser melting (SLM) were investigated with variation of the applied laser scanning speed. The starting materials of Inconel 718 powder particles were prepared using a gas atomization process showing uniform size distribution with high flowability. During the SLM process, the applied scan speed played a decisive role in densification during the SLM process, and that the highest density (>99%) and hardness (320 Hv(0.5)) could be achieved at the laser scanning speed of 800 mm/s. Upon fabrication, the microstructure of Inconel 718 parts was characterized by the presence of columnar grains, due to the rapid rate of cooling of the molten pool. These grains, in particular, in XZ and YZ planes, were observed to be parallel to the building direction (Z-axis), with size ranging from several to hundreds of micrometers. It was also found that the fine cellular substructures, within the specified range between 0.5 and 1 mu m, were embedded inside each large grain with low angle boundaries (<2 degrees). The experimental findings in this study may provide fundamental understanding of densification and microstructural characteristics induced by the laser melting process.</P>