Molding of temperature field for the induction skull melting process of Ti-47Ni-9Nb
- PDF / 559,553 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 105 Downloads / 181 Views
DUCTION Ti-47Ni-9Nb, an important shape-memory alloy, was developed to meet the needs of aerospace and civil applications. The investigations showed that the composition of the alloy has a critical effect on the mechanical properties and shape-memory property. Assuring the composition in the preparation process is the key step in obtaining an alloy with desirable properties. Both powder metallurgy (PM) and ingot metallurgy (IM) are commonly used in the preparation process. The PM process has the advantage in preparing sponge Ti-47Ni-9Nb, but it is difficult to obtain fully compact materials.[1] Another vital problem is the pollution of interstitial elements to the alloy during the PM process.[2] The IM process can produce impact materials, but the ordinary melting methods could not avoid pollution from the ceramic crucible.[3,4] Currently, melting reactive alloys with a cold crucible is a valid method to prevent pollution from the ceramic crucible.[5,6] There are two techniques in common use: vacuum-arc remelting (VAR) and electron-beam melting (EBM). However, these two techniques involve many problems also.[5,7] The induction skull melting (ISM) process has developed rapidly in the last decades. It is suitable for melting reactive alloys, especially for melting intermetallic compounds.[8,9] However, by now, almost all of the work is concentrated on the experimental research; few theoretical research has been carried out or reported, for example, on the melt temperature control. This article focuses on the issue of how to control the melt temperature in the ISM process. This control is very important in predicting the component evaporation process of a TiNi melt under vacuum.[10] YANQING SU, Associate Professor, YUAN LIU and GUIZHONG LIU, Ph.D. Candidates, and JINGJIE GUO, DAMING XU, and JUN JIA, Professors, are with the School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, P.R. China. Manuscript submitted July 26, 2000. METALLURGICAL AND MATERIALS TRANSACTIONS A
II. THE MELTING PRACTICE OF TI-47NI-9NB ALLOYS WITH ISM The ISM furnace used in the study is schematically shown in Figure 1. The heart of the furnace is the crucible, as illustrated in Figure 2. In a solid, water-cooled copper crucible, a large portion of the electromagnetic field generated by the induction coil would be attenuated in the crucible rather than in the charge, and little or no melting of the charge would occur. So, the copper crucible used in ISM is a slotted, water-cooled design, as shown in Figure 2. The crucible is fitted together with many segments and a baseplate. A high-temperature insulative ceramic is packed between the segments and a thin gap remained, which allows the magnetic field to penetrate into the charge. Both the segments and baseplate of the crucible contain internal passageways for cooling water. During melt processing, the charge is melted in the cold crucible, where part of the solid barrier between the molten metal and the cold crucible resolidified from the same metal composition.
Data Loading...
