THE EFFECT OF THE TEMPERATURE OF PLASTIC-DEFORMATION ON THE CHANGE INSTRUCTURE AND MECHANICAL-PROPERTIES OF A SUPERSATURATED CUNI4SI1 SOLID-SOLUTION

The paper presents the results of investigations of the mechanical pro perties and analysis of structural changes in CuNi4Si1 alloy, induced by static and dynamic precipitation. During isothermal ageing the spin odal decomposition and continuous precipitation of fine, coherent Ni2S i precipitates are responsible for the increase of strengthening. Decr ease of strengthening in the later period of ageing takes place as a r esult of the growth of continuous precipitates and the appearance of d iscontinuous precipitates of the same phase. The discontinuous precipi tates have the form of lamellae. Precipitation during plastic deformat ion of CuNi4Si1 alloy at temperatures lower than the solvus temperatur e induces precipitation-strain hardening. The dynamic decomposition of the supersaturated solution is very fast, and the value of the attain ed strengthening is greater than that obtained during static ageing. A pplication of preliminary ageing prior to plastic deformation is respo nsible for the fact that the maximal values of the flow stress at the given temperature are smaller than those for a material without prelim inary ageing. Great strain hardening of CuNi4Si1 alloy is obtained whe n the supersaturated solid solution is subjected before ageing to cold plastic strain (epsilon = 0.15). A still stronger effect of strain ha rdening is attained when the supersaturated alloy undergoes deformatio n (epsilon = 0.15) at the temperature of subsequent ageing.