September AMP_Digital

FEATURE A D V A N C E D M A T E R I A L S & P R O C E S S E S | S E P T E M B E R 2 0 1 8 5 1 19 CHTE UPDAT C HTE’s three-year project is focused on gaining a better understanding of how AM steel alloys respond during post-processing heat treatment such as normalizing, carburizing, and hardening. In their study, selective laser melting (SLM) is used to fabricate the AM parts. SLM, also known as direct metal laser melting, uses a laser as the pow- er source to melt metallic powder successively, based on predesigned computer-aided specifications. This technique binds the material to create a solid structure. Richard Sisson, CHTE’s technical director and George F. Fuller professor of mechanical engineering, explains, “We are doing this research because we need to determine how to heat treat additively manufactured parts to achieve me- chanical properties that are comparable or even better than heat treated, conventionallymanufactured (wrought) parts.” This becomes incredibly important during critical op- erations like those being performed by the military, but it also applies to manufacturers everywhere. According to Mei Yang, assistant research professor on the project and asso- ciate technical director of CHTE, “Companies all over the world are interested in what impact additive manufactur- ing will have on their business. For some of our members, this research is an introduction to additive manufacturing RESEARCHERS EXPLORE HEAT TREATMENT OF ADDITIVELY MANUFACTURED STEEL PARTS Researchers at the Center for Heat Treating Excellence (CHTE) at Worcester Polytechnic Insti- tute (WPI) are working with CHTE members to develop post-processing parameters to enhance the mechanical properties of additively manufactured (AM) steels. TABLE 1 — SELECTED ALLOYS AND MATERIAL PROVIDERS Alloy Material provider Powder As-fabricated Wrought AISI 8620 Company A Company A Company A 20MnCr5 Company A Company A Company A Company B Company B Company B AISI M2 Company B Company B Company A and how it might help their business. For others who have already done major work in this field, it’s an opportunity to learnmore.” Mei Yang and Richard Sisson are working on groundbreaking research that will help heat treaters figure out how to additive- ly manufacture steel parts to better specify post-processing parameters for superior performance. RESEARCH OBJECTIVES It is believed that the response of AM steel parts to heat treatment may be different from that of conventionally manufactured steel parts. As a result, CHTE researchers are working towards understanding the heat treatment process of AM steel parts so they can better determine the heat treat- ment process parameters. CHTE members and researchers selected three steel alloys to test. Alloys were selected based on their broad industry applications andmechanical proper- ties. AISI 8620 and 20MnCr5 will be carburized, while AISI M2 will be quenched and tempered. METHODOLOGY AND CURRENT RESEARCH Selective laser melting is used to fabricate the additive- lymanufactured AISI 8620 parts. The AMparts are carburized and compared to the properties of carburizedwrought parts. Different defects may affect the properties after carburizing. Composition is measured by Optical Emission Spectroscopy (OES) and results are shown in Table 2. The powder chemistry shown in Table 2 is from the powder certificate and the part chemistry is the average of five SLM parts. Carbon shows a decreases of 20% percent in the part compared with the carbon concentration in the powder. To verify decarburization of parts during SLM, the powder was sent to an independent testing laboratory for chemical analysis. Testing showed 0.244 wt% carbon con- centration, which is in agreement with the carbon concen- tration from the powder certificate. Conclusion: Decarburi- zation occurred during SLM.