Effect of crystallization conditions on the structure and phase composition of Ni--Mo alloys

Alloys containing 22 to 44 at.% Mo were crystallized from melts having temperature of 1400, 1900, and 2000 deg C at a cooling rate of 30, 10/sup 4/ to 10/sup 5/, and 10/sup 7/ to 10/sup 8/ deg/s. By cooling at a rate of 10/sup 7/ to 10/sup 8/ deg/s it is possible to suppress the separation of Mo Ni/sub 3/ and MoNi/sub 4/ phases, and attain a higher degree of supersaturation of Mo in the nickel base. In a melt with a content of 34.8 at.% Mo crystallized from a liquid (from 1900 deg C), along with a metastable alpha -solution it was possible to detect a dispersed precipitate of an intermediate metastable gamma '-phase. On increasing the content of Mo to 37.4 at.%, the amount of gamma '-phase increases. This phase has a free crystal lattice with a = 4.255 kX in a melt with a content of 34.8 at.% Mo. The interplanar distances are tabulated. The gamma '-phase is stable on heating to 600 deg C. On holding 2 h at 600 deg C in a furnace with a protective atmosphere, the gamma '-phase transforans into a hexagonal, dense- packed phase close in composition to MoNi/sub 3/.more » At concentrations of 22 to 28 at.% Mo in films cooled at a rate of 10/sup 7/ to 10/sup 8/ deg/s, breakdown of the supersaturated solid solution takes place on heating to 650 deg C for 1 h. At a temperature or 700 deg C for 30 minutes (in a furnace with a protective atmosphere), the compound MoNi/sub 4/ separates out of melts containing 22 to 28 at.% Mo. (SJR)« less