ALLOYS FOR HIGH-TEMPERATURE SERVICE
Abstract
A metallographic and x-ray diffraction study of the Co-Cr binary diagram and a study of the effect of ternary additions were undertaken for a structural analysis of Vitallium alloys. The following sluggish transformation reactions were indicated: (1) Cr and Mo raised the alpha-beta transformation temperature in the Co-Cr systems; (2) N, Fe, and Ni markedly lowered the temperature; and (3) W had little effect. All the ternary additives raised the alpha Co2Cr3 precipitation temperature; the compound precipitated at a low Cr concentration in a spheroid or platelet form. The upper limit (1000 deg. C) of the alpha-beta transformation temperature of Stellite no. 21 was lowered by Ni and raised by C and Mo. Minor phases in Stellite included Co2Cr3, M23C6, M6C, and Cr7C3. Creep-rupture tests on Co-Cr alloys with and without N at 780 deg., 915 deg., and 1000 deg. C indicated that: (1) an increase in the Cr, C, or Ni content increased the strength; (2) alpha and beta phases had about the same strength at elevated temperatures; (3) some alloys had lower creep rates at high stresses than at lower stresses; and (4) an increase in the prestress at a given testing temperature lowered the creep rate. Time-deformation curves probably represented a normal tendency toward creep combined with a contraction tendency resulting from the precipitation of submicroscopic particles. Stellite alloys, subjected to creep-rupture tests at 816 deg. C, were stronger in the as-cast condition than after homogenizing or homogenizing and aging. Minor changes in C, Ni, or Mo had little effect on the aging characteristics. No relationship was found between the rupture strength and hot-hardness.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 30, 1952
- Accession Number
- AD0011576
Entities
People
- A. B. Westerman
- A. R. Elses
- E. E. Fletcher
- G. K. Manning
- R. L. Beck
Organizations
- Battelle Memorial Institute