ASSESSMENT OF THE DURATION OF TIME REQUIRED FOR CONVENTIONAL Ti-Ni SINTERING

Abstract

Elemental blends of Ti-Ni powder in the TisoNiso ratio were tested by the conventional press and sintered method. The sintering conditions employed were based on solid-state diffusion which resulted in a homogeneous alloy exhibiting the shape-memory effect. An attempt has been made to establish a mathematical model to predict the time required for complete homogenization. The comparison of the calculated values with that of the experimental results revealed consistency. Powder metallurgy is an alternative method of manufacturing products which is receiving an ever increasing attention with obvious economic benefits. The importance of this approach lies in the possibility of producing novel materials (such as TiNi), in which conventional' techniques are cumbersome. Sintering of the elemental blend of Ti-Ni powder is an alloying process with the aim to achieve intermetallic compounds of TiNi (I-61. However the concept of sintering of these powders is rather complicated and is dependentoupon the set conditions. If the sintering process is carried out beneath 940 C (which is the lowest eutectic point, see fig. 1). and with a moderate heating rate, the process .will be controlled by solid-state diffusion, otherwise a reactive combustion may prevail (81. It is the aim of this paper to concentrate and study the solid-state diffusion process in this alloy, and attempt is made to predict the homogenization process by employing a mathematical model. Pure Ti and Ni powders having purities of 99.5% and 99.9% respectively with a particle size of -45 pm were employed in this study. The powders were blended in a cylindrical mixer and compacted in an uniaxial mode. The relative green densities of the compacts were 80% of the theoretical value. The compacts prepared had a mean alloy composition of TisoNiso (at%). Sintering was conducted under Argon atmosphere, by .first pre-vacuuming to 10-'~orr, heating up geriod till the final szt temperatur: was selected a:: first heating up to 600 C by 20 Chin, then 10 Chin to 700 C followed by 2 Chin in the range of 750-900 C. The reason for the low heating rate at the last stage is to prevent combustion. All sintered samples were subjected to SEM and X-ray micro-analysis. To detect the transformation characteristics of the samples,