Showing papers by "Defence Metallurgical Research Laboratory published in 1980"

Strengthening mechanisms in alloys

Abstract: Metals can be strengthened by methods appropriately combined to meet the operating conditions. In this ‘alloy design’, effort, we are guided by semi-quantitative relations that have been developed over the years and which relate the efficacy of the strengthening methods to the deformation modes. In this paper, the basic concepts are expanded with specific reference to dislocation glide, diffusional creep, grain boundary sliding and high strain rate deformation.

A reconsideration of phase relations in the Ti-Al-Mo and Ti-Al systems

Abstract: A microstructural and X-ray investigation of Ti-AI-Mo alloys Ti-31 Al-15 Mo, Ti-31 Al-13 Mo, Ti-31Al-9Mo and Ti-35Al-9Mo (containing the Ti3Al, TiAl and β phases) indicates that the existing phase diagram of the ternary system for this composition range published by Ge Dhzhi-Min and Pylaeva is in error above 1473 K An analysis of phase relations reveals that the error has arisen from their use of the Ti-AI diagram due to Bumps, Kessler and Hansen as a basis for generating the ternary It is shown that a phase diagram of the ternary, consistent with the experimental results, can be generated using a version of the Ti-AI system due to Margolin Simple geometric arguments are used to build up a new semi-quantitative description of the Ti-AI-Mo system which can be used as a basis for a detailed investigation of phase equilibria in this system

Inhomogeneous flow and the effective pressure concept in pressure sintering

Abstract: Many of the models proposed to describe pressure sintering of solids with a randomly distributed porosity have implicit in them the effect of porosity and it is incorrect to incorporate any extra pressure intensification factor. However, usually, pores are segregated into zones which leads to inhomogeneous deformation. A consequence of this inhomogeneity is to enhance densification rates by dislocation creep and particle sliding resulting in an anomalous pressure intensification factor. Some observations on microstructural development during hot isostatic pressing are also made.

Structural studies on the alloying behaviour of γ-Mn and the development of a high damping capacity in Mn-Cu alloys

Abstract: Quenched Mn-Cu alloys undergo an unusual type of phase transformation and form metastable structures. A miscibility gap exists in these alloys, and the stability of the alloy phases is associated with the allotropic form of elemental Mn-atoms beyond the equi-atomic compositions. Quenched Mn-33.4 at% Cu alloy, which corresponds to the centre of the miscibility gap, upon ageing gives rise to a high damping capacity. The internal lattice strain which is the cause of the high damping capacity is thought to be due to interfacial misfit of the MnCu phase and elemental Mn in the proposed metastable structure of the alloy.

Strengthening against creep

Abstract: Strengthening alloys against creep deformation involves strengthening against dislocation glide and climb, and grain-boundary sliding. The rationale behind various techniques currently used for strengthening are discussed, especially with reference to Ni-base superalloys. Although one should try and minimize sliding by increasing grain-boundary viscosity, the grains should not be over-strengthened to minimize problems due to creep cavitation.