Accession Number : AD0816137

Title :   EFFECT OF PROCESSING VARIABLES ON THE STRUCTURE AND PROPERTIES OF REFRACTORY METALS.

Descriptive Note : Final rept. 1 Jul 65-31 Mar 67,

Corporate Author : LOCKHEED MISSILES AND SPACE CO INC PALO ALTO CA PALO ALTO RESEARCH LAB

Personal Author(s) : Perkins, R. A.

Report Date : MAY 1967

Pagination or Media Count : 135

Abstract : The control of carbide dispersions and their contribution to the strength and ductility of Cb-TZM(Mo-1.5Cb-0.5Ti-0.3Zr) sheet was investigated. Increasing the carbon content during the latter stages of processing by means of controlled carburization was found to be impractical. The mechanics and kinetics of the carbide interchange reaction (Mo2C yields CbC) which occurs upon heating of solution-annealed alloys at temperatures of 2000 to 3200 F was studied. The process is characterized by the simultaneous dissolution of the Mo2C phase, transport of Cb and C to preferred sites, and precipitation of CbC platelets on the (100) planes of the Mo matrix. Kinetics of the process are strongly temperature dependent and are believed to be governed by the diffusion of Cb atoms. Platelet size and distribution were found to depend largely on time at temperature with a limiting size (maximum) of 0.2 microns wide by 3 microns long attained at temperatures of 2600 to 3200 F. The CbC platelet carbide was stable in long-time exposure at temperatures to 3200 F. However, after straining below the recrystallization range, the CbC platelets were observed to spheroidize in short times upon heating at 2400 to 3200 F. Spheroidization appears to result from an unstable interface condition developed by the pileup and tangling of dislocations at the platelet/matrix interface during straining. Spherical CbC dispersions were found to be far less effective in blocking dislocations and in raising the temperature for recrystallization.

Descriptors :   (*MOLYBDENUM ALLOYS, PROCESSING), CARBIDES, HEAT TREATMENT, CASE HARDENING, NIOBIUM ALLOYS, TITANIUM ALLOYS, RECRYSTALLIZATION, DUCTILITY, BRITTLENESS, CREEP STRENGTH, TENSILE PROPERTIES, DISPERSION HARDENING, STRUCTURAL PROPERTIES, ANNEALING, DEFORMATION, STABILITY, AGING(MATERIALS), ROLLING(METALLURGY), MECHANICAL PROPERTIES.

Subject Categories : Metallurgy and Metallography

Distribution Statement : APPROVED FOR PUBLIC RELEASE