Effect Of Predeformation And Structure Parameters On The Recovery Property Of Ni₄₇Ti₄₄Nb₉Alloy Φ8mm Pipe Joint

NiTiNb shape memory alloys with the wide transformation hysteresis have attracted extensive attentions and studies in the alloy of pipe joint. But recently there was always the problem of improving the transformation hysteresis and enhanceing rocevery rate when NiTiNb shape memory alloy was used to make pipe joint. Thus the system study of the influence of predeformation and structural parameters on the recovery performance of NiTiNb shape memory alloy pipe joint has important significance. This paper used the research method of cryogenic expander、heating in water bath and microstructure observation to study the effect of prestrain temperature, predeformation amount, wall thickness, length and so on on recovery property of Ni47Ti44Nb9alloy pipe joint. The results showed:For different predeformation temperatures, the result showed the transformation hysteresis and residual strain of Φ8mm pipe joint increased first and then decreased when the predeformation temperature went up; the elastic strain of inner diameter, radial recoverable strain and recovery rate decreased first and then increased when the predeformation temperature went up. The best predeformation temperature of Φ8mm pipe joints was-65℃. In this case, the transformation hysteresis, elastic strain, radial recoverable strain, recovery rate of inside diameter were122℃,1.0%,8.6%and86%respectively.For different predeformation amount, the result showed the transformation hysteresis, elastic strain, residual strain of Φ8mm pipe joint increased when the predeformation amount increased. The radial recoverable strain of inside diameter increased first and then decreased when the predeformation amount increased. The recovery rate declined when the predeformation amount increased. The predeformation amount of Φ8mm pipe joints was12.1%. In this case, the transformation hysteresis, elastic strain, radial recoverable strain, recovery rate of inside diameter were130℃,2.7%,8.6%and78%respectively.For different structural parameters, the transformation hysteresis of Φ8mm pipe joints at the inside diameter decreased when wall thickness and length increased. The elastic strain of inner diameter increased when wall thickness increased, and decreased when the length increased. The residual strain of the inner diameter decreased when wall thickness and length increased. Radial recoverable strain of inner diameter increased first and then decreased when wall thickness went up and increased when the length increased. The recovery rate of inside diameter tended to increase when wall thickness and length increased. Finally the best wall thickness and length of the Φ8mm pipe joint were2.1mm and32mm respectively. In this case, the transformation hysteresis, elastic strain, radial recoverable strain, recovery rate of inside diameter were130℃,0.27%,8.0%,66.7%and130℃,0.9%,7.5%,73.6%respectively.The observations of different state organizations of Φ8mm pipe joints indicated the organization of Φ8mm pipe joint was made of NiTi phase and β-Nb phase. The organization of casting NiTiNb increasingly fine after the process of forging→rolling→expanded and so on, and the NiTi phase was squeezed obviously. The organization of the pipe joint was fine at the condition of different predeformation temperature, different predeformation amount, different wall thickness, different length, and existed β-Nb phase in the NiTi phase.The results of above analysis showed that the best predeformation process and structure parameters of Φ8mm pipe joint was that predeformation temperature was-65℃, the predeformation amount was12.1%, the wall thickness was2.1mm, the length was32mm.