Alloying Effect on the Microstructure and Property of Single Crystal Ni 3 Al Alloys
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ALLOYING EFFECT ON THE MICROSTRUCTURE AND PROPERTY OF SINGLE CRYSTAL NI 3 Al ALLOYS Zhang Jinghua, Yu Yang, Zhang Zhiya, Tang Yajun, Zhang Jishan, Li Yingao, Ding Dongsheng and Hu Zhuangql Institute of Metal Research, Academia Sinica, 2-6 Wenhua Rd., Shenyang, P.R.China
ABSTRACT The alloying effects of Cr, Zr, Ta, Nb and B on the microstructure and The strength properties of single crystal Ni 3 Al alloys have been studied. The of the alloys has been improved markedly with promising plasticity. a 0.2% yield stress of some of these alloys is higher than that of IN713C, to typical cast nickel-base superalloy, in the temperature range from 25 9500C and some of them reach the strength level of advanced cast nickel-base The creep strength of alloys such as IN100 in the high temperature range. The single crystal Ni 3 AI alloy with these alloys is also improved markedly. a high Cr content ( 7 at-%) obviously shows an intermediate temperature low Although heat treatment can only slightly improve the plasticity behavior. *strength, it can double the elongation of the alloy from 25% to 50%. In the Ni3Al monocrystal containing 1.2at%Zr there exist great amounts of the low Y/Y' eutectics. This melting point Ni 5 Zr-Y eutectics around the ordinary makes it difficult to homogenize the coarse casting structures completely.
INTRODUCTION As a promising new generation of high performance structural material, the high temperature ordered intermetallic alloys have advantages such as stable microstructure and higher oxidation lower density, higher strength, resistance [1,2 1. The study of these alloys has drawn the attention of many scientists. In order to improve the comprehensive properties of these alloys, modern alloy design theory and various modern processing techniques The have been applied to design and control the structures of the alloys. single crystal processing technique plays an important role in the development of new and high performance superalloys [3,4]. Alloy design for single On crystal alloys is different from that for the polycrystalline alloys. the basis of many years of research on the directional solidification and single crystal superalloys, we have selected the well characterized Ni3AI alloy to study the application of the single crystal processing techniques in this field and the special alloying requirements for the single crystal Ni3AI alloys.
EXPERIMENTAL Table 1 shows the compositions of the intermetallic Ni3Al alloys studied. First, a 20kg master alloy ingot with the composition of Alloy A was produced Then, the single crystal specimens by vacuum induction melting processing. with different compositions were produced by adding proper alloying elements The single crystals of 1.6 cm in during single crystal growth processing. diameter and 7.5 cm in length were grown by HRS process under the conditions 0 of thermal gradient about 87 C/cm and pulling rate about 1 mm/mmn. 1 were made in the temTensile tests with strain rate of about lxlO-3s0 Stress-rupture test were perature range from room temperature to
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