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 | O C T O B E R 2 0 1 5
HEAT TREATING ADDITIVELY MANUFACTURED
Applications in additive manufacturing (AM), also
known as 3D printing, are growing, especially in the biomed-
ical industry where individually customized parts such as hip
joints, knee replacements, anddental applications are inhigh
demand. The Center for Heat Treating Excellence (CHTE) at
Worcester Polytechnic Institute (WPI), Mass., is studying the
best way to heat treat these parts for optimumperformance.
“Because these components become a part of our bod-
ies, we need to determine how to post-process them to re-
move defects that can initiate fatigue fractures, resulting in
a deterioration in themechanical properties of thematerial,”
says Richard Sisson, WPI professor of mechanical engineer-
ing and technical director of CHTE.
Titanium and titanium alloys, cobalt alloys, and stain-
less steels are the fourmain types ofmetallic biomaterials. Ti-
taniumalloys arepreferred indental andorthopedic implants
due to their good mechanical properties, biocompatibility,
lack of allergic reaction, and excellent corrosion resistance.
WPI graduate student Yangzi Xu, under the direction of
Sisson, is investigating the effects of heat treatment on themi-
crostructure, mechanical properties, and corrosion behavior
of additively manufactured Ti-6Al-4V titanium alloy parts fab-
ricated using the direct metal laser sintering (DMLS) process.
DMLS uses a laser as the power source to sinter successive lay-
ers of metal powder based on a computer-aided design. The
technique binds the material together to create a solid struc-
ture. Three post heat treatments being investigated include
solution treatment and aging, stress relieving, and annealing.
Evaluation of parts includes measuring microindenta-
tion hardness, determining microstructure and phase evo-
lution using scanning electron microscopy and x-ray diffrac-
tion, and electrochemically measuring corrosion behavior in
simulated body fluid at a temperature of 37°C (98.6°F). Re-
search results of the study are expected in 2016.
The CHTE collaborative is an alliance between the indus-
trial sector and university researchers to address short-term
and long-term needs of the heat-treating industry. Member-
ship in CHTE is unique because members have a voice in se-
lecting quality research projects that help them solve today’s
Research projects are member driven. Each research
project has a focus group comprising members who provide
an industrial perspective. Members submit and vote on pro-
posed ideas, and three to four projects are funded yearly.
Companies also have the option of funding a sole-sponsored
project. In addition, members own royalty-free intellectual
property rights to precompetitive research and are trained on
all research technology and software updates.
CHTE projects now in progress include:
Nondestructive Testing for Hardness and
Improving Furnace Alloys and Fixtures
Gas Quench Steel Hardenability
CHTE is located in Worcester, Mass., on WPI’s New En-
gland campus. The university was founded 150 years ago this
year. For more information about CHTE, its research projects,
and member services, visitwpi.edu/+chte
, call 508.831.5592,
or email Rick Sisson email@example.com
, or Diran Apelian firstname.lastname@example.org
Surrounded by a traditionally cast metal part, Diran Apelian,
director of WPI’s Metal Processing Institute, holds an intri-
cate metal object fabricated layer by layer using additive
Other AM-related research is also underway in the
areas of modeling, surface finishing, and new AMmaterials.
Sisson is developing databases and computational
models to understand and predict the properties and per-
formance of materials created using cold spray, a related AM
process. The multiyear research program is funded by the
U.S. Army Research Laboratory (ARL). ARL uses cold spray to
repairmagnesiumgearboxes in helicopters andwould like to
use AM to produce entire replacement parts for its vehicles.
Associate professor of mechanical engineering Jianyu
Liang and her research team are exploring electrochemical
finishing techniques that can reduce the vulnerability of AM
parts to fatigue and cracking.
Diran Apelian, director of WPI’s Metal Processing In-
stitute, is collaborating with researchers at Lawrence Liver-
more National Laboratory in California (a CHTE member)
to explore thixotropic metals that remain semisolid across
a range of temperatures. By manipulating both tempera-
ture and shear, researchers hope to achieve the kind of pre-
cision required to additively manufacture complex metal
To learn more about AM research at WPI, visithttp:// wpiresearch.epubxp.com/i/502587-spr-2015