Hits:

Indexed by:期刊论文

Date of Publication:1993-02-01

Journal:JOURNAL OF THE JAPAN INSTITUTE OF METALS

Included Journals:SCIE

Volume:57

Issue:2

Page Number:220-227

ISSN No.:0021-4876

Key Words:NIAL; INTERMETALLIC COMPOUND; DEFECT STRENGTHENING; BORON ADDITION; OFF-STOICHIOMETRY

Abstract:The defect strengthening due to the deviation from stoichiometry and the solution hardening by the addition of boron have been investigated in NiAl alloys and the results are compared with the available data for other B2 type intermetallic compounds. It is found that the defect strengthening in NiAl alloys cannot be interpreted solely by the conventional solid solution hardening theory in dilute alloys. By comparison with the results for other B2 type compounds, it is deduced that the degree of defect strengthening is larger in a compound having less compositional range in the binary equilibrium phase diagram within which the B2 structure is stable. These observations imply that in NiAl alloys the defects introduced by the deviation from stoichiometry would heterogeneously be distributed resulting in the formation of some kind of atomistic region in which the solutes are in a short or long range ordereded state. This might be the reason for the excess strengthening over the case for a dilute solution with homogeneous distribution of solutes. The effect of 0.05 mass% boron is found to increase both the lattice parameter and the hardness of NiAl in its Ni-rich compositions, while there is no such effect for the Al-rich deviation from stoichiometry. In the Ni-rich alloys, boron atoms dissolves interstitially and the excess atoms forms borides, while in the Al-rich alloys they all segregate to the grain boundary and do not exist nearby or in the structural vacancies.