 Author to whom all correspondence should be addressed. * Also Beijing Laboratory of Electron Microscopy, Chinese Academy of Sciences, P.O. Box 2724, Beijing 100080, People’s Republic of China. JOURNAL OF MATERIALS SCIENCE 32 (1997) 4723 — 4729 Microstructure of TiNi shape-memory alloy synthesized by explosive shock-wave compression of Ti – Ni powder mixture XIAODONG HAN *  Department of Materials Science, Dalian University of Technology, Dalian 116024, People’s Republic of China WENHUI ZOU * , RENHUI WANG * Department of Physics, Wuhan University, Wuhan 430072, People’s Republic of China SING JIN, ZE ZHANG Beijing Laboratory of Electron Microscopy, Chinese Academy of Science, Beijing 100080, P.O. Box 2724, People’s Republic of China TONGCHUN LI, DAZHI YANG Department of Materials Science, Dalian University of Technology, Dalian 116024, People’s Republic of China Cylinders of TiNi shape-memory alloy were synthesized from mixtures of equiatomic fine irregular titanium and nickel powders by explosive-wave compression with a detonation velocity of about 6500m s1. B2 type parent phase, R phase, B19 type martensite, Ti 2 Ni, Ti 3 Ni 4 and Ti 2 Ni 3 phases were observed in this as-synthesized material. In the B2 matrix high density dislocations existed. The Burgers vectors of many dislocations were determined to be parallel to 111 directions. The R phase variants formed (001) B2 twinning structure. The substructure of the B19 martensite was (001) B19 type I twin and stacking faults on the (00 1) B19 plane. When increasing the temperature of the as-synthesized material in a differential scanning calorimeter, no B19 PRPB2 transitions were observed on the temperature range !50 to 100 °C. However, B2 PB19(R) transitions occurred during the cooling cycle. After heat treating the specimen at 800 °C for 1 h and then ageing at 400 °C for 10 min, both B2 PRPB19 and B19(R) PB2 phase transitions were observed. 1. Introduction TiNi shape-memory alloy (SMA) is an excellent func- tional material. It has many good characteristics, such as perfect shape-memory effect (SME), superelasticity and high corrosion resistance. However, its high price, resulting from complicated and difficult melting and machining procedures, have limited its application. In order to utilize TiNi SMA cheaply and widely, many manufacturing methods, such as powder metallurgy [1], self-propagating high-temperature synthesis (SHS) [2], which can omit many complicated pro- cesses, have been tried. In recent years, explosive shock-initiated chemical reactions are of considerable interest. With the high temperature and pressure asso- ciated with shock-wave processing, it may concurrent- ly synthesize and form net-shaped parts of intermetal- lic compounds and other materials from elemental powders. Shock compression of powders produces an unusual combination of ‘‘structure defects’’ and ‘‘powder packing characteristics’’ that can significantly promote chemical reactivity of powders and lead to accelerated mass transport kinetics. Under such unique conditions, not only can metal and ceramic powders be dynamically consolidated [3, 4], or undergo solid- state phase transformation [5], but also molecular decomposition of compounds can occur [6], as well as chemical reactions in bonding mixtures [7], resulting in the synthesis of compounds. We have tried a technique of obtaining TiNi SMA directly by means of explosive shock-wave compression which induce chemical reac- tion in an equiatomic Ni/Ti powder mixture. The detailed microstructure and phase transformation be- haviour of the synthesized alloy are reported. 2. Experimental procedure Irregular titanium powders and nickel powders were used in this study. The powders were of a commercially 0022—2461  1997 Chapman & Hall 4723