TUNGSTEN SOLUTION KINETICS AND AMORPHIZATION OF NICKEL IN MECHANICALLY ALLOYED NI-W ALLOYS

The kinetics of solution of W, and the subsequent amorphization of Ni, in mechanically alloyed Ni-W alloys has been investigated. As W is a highly abrasive material in the energy intensive devices used for mechanical alloying, we studied the above reactions in different mills. One used hardened steel balls as the grinding media, and the other Al2O3. Abrasion is common to both mills, but Fe wear debris from the hardened steel enters into solution in the Ni rich phases whereas Al2O3 debris is present as small dispersoids. The kinetics of W solution and those of subsequent amorphization do not appear strongly affected by the Fe in solution or the Al2O3 dispersoid. Tungsten dissolves in crystalline Ni in amounts in excess of the equilibrium solubility during alloying. Amorphization of the Ni phase occurs if the W content in this phase exceeds ca. 28 at.%. The kinetics of W solution in the crystalline Ni phase and of amorphization can be followed by X-ray analysis. The subsequent crystallization products, obtained by heating the amorphous phase to temperatures greater than about 1000 K, are primarily the intermetallic compounds Ni4W and NiW.