Abstract
A comprehensive study was conducted on microstructural evolution of sintered Ti-Al-V-Fe titanium alloys utilizing very fine hydrogenation-dehydrogenation (HDH) titanium powder with a median particle size of 8.84 μm. Both micropores (5–15 μm) and macropores (50–200 μm) were identified in sintered titanium alloys. Spherical micropores were observed in Ti-6Al-4V sintered with fine Ti at the lowest temperature of 1150 °C. The addition of iron can help reduce microporosity and improve microstructural and compositional homogenization. A theoretical calculation of evaporation based on the Miedema model and Langmuir equation indicates that the evaporation of aluminum could be responsible for the formation of the macropores. Although reasonable densification was achieved at low sintering temperatures (93–96% relative density) the samples had poor mechanical properties due mainly to the presence of the macroporosity and the high inherent oxygen content in the as-received fine powders.
Highlights
IntroductionThe sintering data compiled by Robertson et al confirms that a finer particle size is beneficial for titanium powder densification [2]
Sintering is by far the most common consolidation method in titanium powder metallurgy.The initial stage of sintering can be empirically modeled in terms of isothermal neck growth as measured by the neck size ratio X/D [1]:( X/D )n = Bt/D m (1)where D is the particle diameter, X = neck diameter, t = isothermal sintering time, and B is a collection of material and geometric constants
The micrographs of as-received powders are shown in Figure 2 including fine titanium, iron
Summary
The sintering data compiled by Robertson et al confirms that a finer particle size is beneficial for titanium powder densification [2]. Titanium powders with very fine particle size are not usually available, if a low impurity level is required. A recent study reports a novel technique to produce titanium powder with a mean particle size of 0.8 wt %) [6]. It is known that high oxygen content can adversely affect mechanical properties, especially ductility [4,5,7], and the aim of this research is primarily to investigate the feasibility of using a very fine titanium powder
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