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Title

SINTER B0NDING TITANIUM POWDER COMPONENTS: AN UNCONVENTIONAL ADDITIVE MANUFACTURING APPROACH

Creator

Montonera, Darrell R

Date

2018, 2018-05

Description

Titanium and its alloys are desirable for many applications. The cost of producing titanium parts that also have needed microstructure for a...
Show moreTitanium and its alloys are desirable for many applications. The cost of producing titanium parts that also have needed microstructure for a given application limit where titanium is used. Methods of reducing the cost of titanium parts have been to use powder metallurgy processing routes. However, not all powder processing routes are cost effective, as additive manufacturing and powder injection molding processes are costly and require expensive spherical powder. Cheaper processing Press and Sinter utilizes cheaper non-spherical powder. Powder titanium components made through Press and Sinter have complexity, size, and geometrical constraints and have detrimental mechanical properties unless further post processing is done. To utilize the simple geometries from Press and Sinter, pressed powder components are bonded to examine the possibility of creating higher complexity parts. To achieve this, the dimensional sintering behavior of powders were quanti- ed using dilatometry. Grade 5 titanium alloys were created by blending hydridedehydride (HDH) commercially pure powder with master alloy (MA) 60/40 wt%. The dimensional effect of varying master alloy produced a maximum difference of 0.341% between an alloy with lower MA content compared to higher content during sintering. The sintering behavior of powder HDH+MA reached a nal shrinkage of 4.59%. Other powders TiH2, TiH2+MA, and Armstrong pre-alloyed had fi nal shrinkages of 9.85, 9.64, and 8.31%. The larger shrinkage powders were pressed into a peripheral component to be bonded to a HDH+MA core. Samples were sintered under a vacuum of 2x10􀀀6 torr by heating from room temperature to 1370 oC at 15 oCmin􀀀1 and holding at 1370 oC for 90 minutes. Sinter Bonded sample interfaces were examined showing the best bond to be the Armstrong j HDH+MA combination. This bond was tested using a push out test achieving shear stresses of 423 60 MPa using a pre-sintering tolerance between components of 0.065 mm and 444 37 MPa using a pre-sintering tolerance of 0.03 mm. Wrought material tested in the same manner as the sinter bonded components had a strength of 517 8 MPa. Sinter bonded samples achieved on average 82% the strength of wrought tested in the same manner. Strong bond strengths lead to a fatigue analysis of sinter bonded samples. Under various applied cyclic compressive stresses the number of cycles to failure were measured using an applied stress ratio R = 0.1. Determination of fatigue properties was done by simulating and probing in Abaqus the max tension stresses located at the bottom center of the sample. Simulations produced steady state tension stresses measured at maximum, mean, and minimum applied compressive stresses. These stresses were used to plot a S-N curve. True stress amplitudes were calculated from probed maximum and minimum stresses and the fatigue data were fi t to the Basquin empirical relation 2 = 810:4(2Nf )􀀀0:055 for sinter bonded samples and 2 = 1290:9(2Nf )􀀀0:065 for wrought samples. As a proof of concept several pressed titanium parts were combined in the green state and successfully sintered into a single component.
Ph.D. in Materials Science and Engineering, May 2018
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