Production and Characterization of Metastable-Beta Type Ti-4Fe-3Cr-3Cu Alloy
Eren Burak Capali
Metallurgical and Materials Engineering Department, Istanbul University-Cerrahpasa, Istanbul, Turkey.
Ilven Mutlu *
Metallurgical and Materials Engineering Department, Istanbul University-Cerrahpasa, Istanbul, Turkey.
*Author to whom correspondence should be addressed.
Abstract
In this study, precipitation hardenable metastable-beta type Ti-4Fe-3Cr-3Cu alloy specimens were produced by mechanical alloying-powder injection moulding method for aviation applications such as aircraft engine component or aircraft structural material. In the Ti alloys, important parameter for the beta-titanium phase stability is the molybdenum equivalency (MoE) value, which is a key parameter in the design and development of the composition of beta titanium alloy because it determines the amount of metastable beta-titanium phase. In the present study, MoE value of Ti-4Fe-3Cr-3Cu alloy was in the range of metastable-beta region. In this study, metastable beta-type titanium alloys composed of low density, low cost alloying elements such as Fe, Cr and Cu were designed and developed using a new alloy design method based on molecular orbital calculation (Bo-Md method). Employing the Bo-Md method, it is possible to predict the phase stability, Young’s modulus, and plastic deformation mechanism of the titanium alloys. In the present study, MoE value of Ti-4Fe-3Cr-3Cu alloy was calculated as 21 MoE, which is in the range of metastable-beta titanium region. After calculation, the (Bo, Md) values of the Ti-4Fe-3Cr-3Cu alloy are (2.763, 2.302), which confirms that the Ti-4Fe-3Cr-3Cu alloy is in the beta-titanium phase region in the Bo-Md diagram. In the present study, initially metal powder mixture was mechanically alloyed in a ball-mill. Secondly, mechanically alloyed Ti-4Fe-3Cr-3Cu alloy powders were shaped by powder injection moulding (PIM) method. Binder consisted of 77% polyethylene, 23% paraffin. Feedstock consisted of 46% of binder and 54% of Ti-4Fe-3Cr-3Cu powder. Polymer binder was removed by chemical and thermal debinding. Lastly, Ti-4Fe-3Cr-3Cu alloy specimens were sintered at 1250 ºC. Sintered Ti-4Fe-3Cr-3Cu specimens were annealed, quenched and aged (precipitation hardening). Effects of aging temperature on the mechanical and corrosion properties were investigated. Compressive strength of the Ti-4Fe-3Cr-3Cu alloy was increased with increasing aging temperature and have shown superior properties at 480 °C. Cu addition was enhanced the sinterability of the Ti-4Fe-3Cr-3Cu alloy by liquid phase formation. Electrochemical corrosion rate of the Ti-4Fe-3Cr-3Cu alloy was increased with aging.
Keywords: Precipitation-hardening, titanium alloy, aviation, powder injection moulding