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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

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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

business challenges.

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

Induction Tempering

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, visit

, call 508.831.5592,

or email Rick Sisson at

, or Diran Apelian at


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, visit