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Effect of Reacted Compounds in Al2O3+Ti Investment Mold on Alpha-Case Formation for Ti Casting
최봉재,김영직 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.3
This paper proposes a newly developed alpha-case controlled mold material for Ti castings. An Al2O3mold containing alpha-case reaction compounds, titanium oxide (TiO2, Ti2O and Ti6O) and titanium silicide (Ti5Si3) was manufactured via a reaction between Al2O3 and Ti powder under different firing conditions in air and a vacuum. In comparison with the Al2O3 and Al2O3+Ti mold fired in a vacuum, the micro-Vickers hardness and nano indentation profiles of Al2O3+Ti indicated that the alpha-case thickness was significantly reduced from 350 μm to ~45 μm. The alpha-case formation in the Al2O3+Ti mold was reduced due to the presence of TiO2, which formed the TiO intermediate phase that acted as a diffusion barrier. In addition, Ti5Si3 was effective in minimizing Si contamination at the casting surface due to the reaction between Ti and the colloidal SiO2 binder. Therefore, alpha-case reaction compounds, such as TiO2 and Ti5Si3 in Al2O3, can effectively reduce alpha-case formation at the casting surface.
(TiB+TiC) 입자강화 Ti기 복합재료의 접촉하중에 따른 내마모 특성
최봉재,Choi, Bong-Jae 한국주조공학회 2017 한국주조공학회지 Vol.37 No.4
The aim of this research is to evaluate the wear properties of (TiB+TiC) paticulate reinforced titanium matrix composites (TMCs) by in-situ synthesis. Different particle sizes (1500, $150{\mu}m$) and contents (0.94, 1.88 and 3.76 mass% for Ti, 1.98 and 3.96 mass% for the Ti6Al4V alloy) of boron carbide were added to pure titanium and to a Ti6Al4V alloy matrix during vacuum induction melting to provide 5, 10 and 20 vol.% (TiB+TiC) particulate reinforcement amounts. The wear behavior of the (TiB+TiC) particulate reinforced TMCs is described in detail with regard to the coefficient of friction, the hardness, and the degree of reinforcement fragmentation during sliding wear. The worn surfaces of each sliding wear condition are shown for the three types of wear studied here: transfer layer wear, particle cohesion wear and the development of abrasive areas. The fine reinforcements of TMCs were easily fragmented from the Ti matrix as compared to coarse reinforcements, and fragmented debris accelerated the decrease in the wear resistance.