Compaction of Titanium Powders

Abstract

Accurate modeling of powder densification has been an area of active research for more than 60 years. The earliest efforts were focused on linearization of the data because computers were not readily available to assist with curve-fitting methods. In this work, eight different titanium powders (three different sizes of sponge fines <150 lm, <75 lm, and < 45 lm; two different sizes of a hydride-dehydride [HDH]<75 lm and<45 lm; an atomized powder; a commercially pure [CP] Ti powder from International Titanium Powder [ITP]; and a Ti 6 4 alloy powder) were cold pressed in a single-acting die instrumented to collect stress and deformation data during compaction. From these data, the density of each compact was calculated and then plotted as a function of pressure. The results show that densification of all the powders, regardless of particle size, shape, or chemistry, can be modeled accurately as the sum of an initial density plus the sum of a rearrangement term and a work-hardening term. These last two terms are found to be a function of applied pressure and take the form of an exponential rise.

Analysis of the Cold Compaction Behavior of Titanium Powders: A Comprehensive Inter-model Comparison Study of Compaction Equations

“…Others have also extended this comparison to cover other powder materials [11] The compactibility of Ti-6Al-4V prepared via PM PM Ti-6Al-4V blends (up to 1200 MPa) the compactibility of Ti6Al4V alloy powder produced via the PM route has also been reported. [1,8,12,15] Angular morphologies (and mostly HDH) produced Ti-6Al-4V alloy powder show better compactibility than alloy powder produced from atomized Ti powder in general…”

“…[27] Eventually, according to Bockstiegel, [28] the interest shifted more towards an analytical problem-finding a simple but adequate mathematical description for experimentally observed compaction curves. [1,2,[6][7][8][9][10][11][12][13][14] The compaction curves for ITP-produced Ti, [12] CSIR-produced Ti, [8] Ho¨gana¨s AB produced Ti and TiH 2 , [13,17] Armstrong produced Ti and Ti-6Al-4V, [14,17] spray-dried powders, [20] for example, have also been reported Comparing the compressibility of different powder CP-Ti, sponge, HDH, and various Ti-6Al-4V powder mixtures (up to 1200 MPa) several researchers, see Refs. 1, 2, 6 through 9, 11 through 13, and 17 for example, have also studied and compared the compaction behavior of different Ti powder.…”

“…Lou and Gabbitas [22] insightfully applied empirical compaction equations to evaluate the effects of lubrication Gerdemann and Jablonski [12] systematically studied Ti sponge powder, HDH Ti powder, an atomized Ti powder, an ITP CP-Ti powder, and a Ti-6Al-4V PM alloy powder. Several other researchers have also investigated the variation of compressibility with particle morphology and challenges associated with pressing gas atomization produced spherical powder, see Refs.…”

“…[4,5] Several studies in literature have established relationships between the compaction pressure, the powder characteristics (such as impurity levels and particle size shape), different compaction route (cold, hot, or dynamic compaction), and the obtained properties of the compacts (density, sinterability and strength) with varying degrees of success. [1,2,[6][7][8][9][10][11][12][13][14][15][16][17][18] Studies into the cold compaction of titanium and titanium-based powder materials are necessitated by fact that titanium PM also offers improved chemical homogeneity and refined microstructures [2] in addition to a cost and energy-consumption reduction benefit-given the high cost of titanium powder material. In addition, challenges associated with titanium powder compaction such as (i) the obvious high reactivity of titanium powder material in air, (ii) its inherent difficulty to press into green bodies due to its high hardness and inductile properties, [13] (iii) problems associated with compact cold welding to the die wall [9,11,13,14,19] as well as (iv) the high ejection force required.…”

“…Some noteworthy findings from literature are summarized in Table I. According to Table I, many research articles have reported on the compressibility behavior of titanium powders [1,2,[6][7][8][9][10][11][12][13][14]17,20,22,25] ; evidently, only a very few have paid particular attention to the analysis of the cold compaction behavior of titanium powders using existing or new compaction equations, see References 10,12,14,22, and 25 for example. Those that have, for unspecified reasons, have selectively applied only a few models.…”