Effect of betatizing on grain growth and transformation characteristics of a CuAlNiSMA ribbon with fiber structure

Abstract

The microstructural changes and transformation characteristics with betatizing time were investigated in a Cu-12.7wt%A1-3.9wt%Ni SMA ribbon with fiber structure. The grain growth exponent(n) is 1.2 below a betatizing time of 10(2) sec, and n is 4.6 at longer betatizing times. The significantly reduced n value below 102 see is caused by the higher mobility of straight boundaries in the fiber structure. Most of the parent phase retained in the as-spun ribbon disappears even after flash betatizing at 973 K for 10 sec due to an increase of the degree of L2(1) ordering. Both M-s and A(s) temperatures are abruptly risen but the transformation hysteresis is gradually decreased until betatizing time of 10(2) sec. With further increase in betatizing time, the change in M-s and A(s) temperatures becomes smaller and results in constant value. The M-s temperature of the betatized ribbon is close to that of the mother alloy because of the high surface/volume ratio of melt-spun ribbon.