Engineering topics
Publications and source records attributed to Keh-Minn Chang.
New γ' strengthened nickel-base superalloy compositions are described that, when forged and properly heat treated, demonstrate superior resistance to fatigue crack growth accompanied by very good high temperature properties. Parts can be fabricated (e.g., using conventional cast and wrought processing) from these alloys without encountering difficulty in forging.
It has been found that tri-nickel aluminide compositions are quite sensitive to the ratio of nickel to aluminum in their ability to receive boron as a dopant and that compositions which are relatively poor in the aluminum component can be doped more effectively with boron. Further, it has been found for the nickel aluminides which have lower concentrations of aluminum that the percentage of boron which can be added to the composition to effectively increase the strength of the alloys is . favored by the lower aluminum ratio so that higher concentrations of boron are addable. The compositions which result have significant strength properties based on tensile tests of the compositions.
A method for achieving both improved high strength and improved ductility ·in intermediate phases is provided. The method, briefly stated, comprises the steps of providing a melt whose composition substantially corresponds to that of a preselected intermetallic phase having a crystal structure of the L1 2 type, such as nickel. aluminide, modified with from about 0.01 to 2.5 atomic percent boron, and rapidly solidifying the melt at a cooling rate of at least about 10 3 ° C./second to form a solid body, the principal phase of which is of the L1 2 type crystal structure in either its ordered or disordered state.