Ni <sub> 3 </ Sub> Preparation Of Al Alloys And The Grain Boundary Structure,

This subject is a part of the item — The Study of the Boundary Structureand Strength of Ni₃Al Bicrystal — supported by the national educationcommittee's funds for oversea students. This paper places particular emphasison the preparation of samples, including vacuum melting of Ni₃Al mother alloy,directional solidification of Ni₃Al monocrystal and vacuum diffusion welding ofNi₃Al bicrystal etc. It also preliminarily probes into the boundary structure ofNi₃Al polycrystal. The present results are summarized as follows:l) Ideal Ni₃Al mother alloy can be produced by using the vacuum inductionfurnace of the type ZGJL0.0l-40-4. The raw materials are made up of Ni- 86.4wt% and Al-13.6wt%. The limit of vacuum is below 10^-3Pa. The voltage and thevariable frequency are 280V and 4KHz respectively.2) In Ni₃Al polocrystal, large-angle grain boundary holds a dominantposition. It can be found that annealing decreases the boundary angle in cross-section by comparing the grain angles in annealing Ni₃Al with original castingNi₃Al.3) In the case of high temperature annealing and high temperatureannealing with deformation, the growth speed of Ni₃Al is very slow, whichindicates that it is not a successful way to prepare Ni₃Al bicrystal by polocrystal'sabnormal grain growth.4) Ni₃Al monocrystal can be prepared by means of Bridgman directionalsolidification. The processing concerned is: melting at 1500℃ (at l000℃ Argonis introduced in order to protect the alloy), after selecting crystal by a cylindricalselecting implement(which diameter is bellow two millimeter), directionallydrawing at the speed of l0 μ m/s.5) Using TDR-40 monocrystal furnace Ni₃Al bicrystal can be prepared bymeans of diffusion welding. The process is: preparatory pressure to more than0.4MPa, pumping the vacuum beforehand to the maximum limit, increasing thevoltage by steps to 64V, holding it for eight hours and cooling in the furnace tothe room temperature.