Mechanical properties, fracture behavior, and grain-boundary chemistry of B-doped NiAl

Conference · Mon Jan 01 04:00:00 EST 1990

OSTI ID:6618322

George, E P; Liu, C T ^[1]; Liao, J J ^[2]

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1. Oak Ridge National Lab., TN (USA)
2. Auburn Univ., AL (USA). Dept. of Materials Engineering

This paper summarizes the results of our work aimed at overcoming the intrinsic grain-boundary weakness of NiAl by microalloying with boron. In previous work we have shown that 300 wppm boron is very effective in suppressing intergranular fracture in NiAl. It does this by segregating strongly to the grain boundaries and strengthening them. Despite this dramatic effect on the fracture mode, however, boron is unable to improve ductility because it is a potent solid solution strengthener, more than doubling the yield strength relative to that of undoped NiAl. The present work attempts to decrease this deleterious hardening effect by lowering the bulk concentration of boron in NiAl. Our results show that if the boron concentration in the bulk is lowered to 30 wppm, the yield strength of boron-doped NiAl is only about 30% higher than that if undoped NiAl. In addition, there is enough boron at the grain boundaries of this alloy to suppress intergranular fracture. Under these conditions, boron-doped NiAl has a tensile ductility of 2%, which is essentially identical to that of undoped NiAl. This result, namely that the strengthening of grain boundaries might well be the weakest links in NiAl, cleavage planes are not much stronger. In other words, even though boron additions serve to strengthen the grain boundaries and suppress intergranular fracture, ductility is note improved, because the next brittle fracture mode, namely transgranular cleavage, takes over before significant plastic deformation can occur. 18 refs., 2 figs., 2 tabs.

• Research Organization: Oak Ridge National Lab., TN (USA)
• Sponsoring Organization: DOE/CE
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 6618322
• Report Number(s): CONF-901105-3; ON: DE90015153
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360101 -- Metals & Alloys-- Preparation & Fabrication
360102 -- Metals & Alloys-- Structure & Phase Studies
360103* -- Metals & Alloys-- Mechanical Properties
ALLOYS
ALUMINIUM ALLOYS
BERYLLIUM ADDITIONS
BERYLLIUM ALLOYS
BORON
BORON ADDITIONS
BORON ALLOYS
BRITTLENESS
CARBON ADDITIONS
COMPARATIVE EVALUATIONS
CRYSTAL STRUCTURE
DOPED MATERIALS
DUCTILITY
ELEMENTS
ELONGATION
EXTRUSION
FABRICATION
FRACTURE MECHANICS
GRAIN BOUNDARIES
HARDENING
INTERMETALLIC COMPOUNDS
MATERIALS
MATERIALS WORKING
MECHANICAL PROPERTIES
MECHANICS
METALLURGICAL EFFECTS
MICROSTRUCTURE
NICKEL ALLOYS
SEMIMETALS
STOICHIOMETRY
TENSILE PROPERTIES