CAVITATION EROSION OF NITI EXPLOSIVELY WELDED TO STEEL

Equiatomic and near-equiatomic NiTi alloys are much more resistant to cavitation erosion than even the best stainless steels used in hydraul ic machinery. Since building large components entirely of NiTi is quit e impractical, structural steel was explosively clad with thin layers of NiTi and the cavitation-erosion behavior of NiTi welded to steel wa s investigated. Martensitic NiTi in the as-welded condition proved to be as resistant to cavitation as it was before it was welded, and post -weld heat treatment diminished the resistance slightly. In contrast, austenitic NiTi was significantly less resistant to cavitation after w elding. A post-weld heat treatment of 500 degrees C restored most of t he lost resistance, but heat treatment at 700 degrees C did not. Analy sis of the results indicates that the deformations induced in NiTi by cavity implosions are mostly in the reversible regime, i.e., very litt le damage accumulates from each stress pulse. Comparisons to other ero sion-resistant materials are also presented.