Browsing by Author "R.P. Wahi"

Now showing 1 - 7 of 7

A modified technique for preparing disk specimens for transmission electron microscopy
(1968) R.P. Wahi; D.L. Bhattacharya; T.R. Anantharaman
This note describes a modified 'holder technique' for preparing thin metal foils for transmission electron microscopy. In this, profiling of the sample and determination of the exact moment of perforation are carried out relatively more easily than in the earlier techniques.
Comments on the proposed formation of stacking faults in an AlZn alloy during high-temperature ageing
(1971) R.P. Wahi; P.Rama Rao; T.R. Anantharaman
[No abstract available]
Life prediction for a nickel base alloy nimonic PE 16 under low cycle fatigue loading at 923 K
(1991) M.D. Matthew; V. Singh; W. Chen; R.P. Wahi
The fatigue life of a nickel base alloy Nimonic PE 16 under low cycle fatigue loading with and without hold time has been studied. Introduction of hold time leads to cavitation damage at grain boundaries and lowers the fatigue life. Different life prediction models based on the concepts of hysteresis energy, strain range partitioning and micromechanistic damage have been applied to analyse the experimental fatigue life data. © 1991.
Microstructural stability in a Cu-Cr-Si alloy under 300 keV Cu+ ion irradiation
(1991) C. Ramachandra; N. Wanderka; R.P. Wahi; H. Wollenberger
The stability of precipitate phases in a Cu-base alloy under irradiation with 300 KeV Cu+ ions has been investigated. The irradiations were carried out in the temperature range of 200°C to 530°C at displacement rates of 2.3 × 10-2 and 2.3 × 10-5 dpa/s, respectively. Of the two types of precipitates which form in this alloy under thermal ageing, the metastable. coherent precipitates of fcc chromium either do not form or dissolve, if already present, under most irradiation conditions. The second population of precipitates, i.e. incoherent particles of the stable phase Cr3Si, grow to a temperature dependent stable size under all irradiation conditions. The results are interpreted in terms of mechanisms of cascade mixing and radiation enhanced diffusional growth. © 1991.
On the cyclic stress-strain behaviour of a Ni-base superalloy at room temperature
(1988) Vakil Singh; W. Chen; H.M. Yun; R.P. Wahi
[No abstract available]
Radiation-altered phase stability of a precipitate-hardened copper alloy
(1992) N. Wanderka; C. Ramachandra; R.P. Wahi; H. Wollenberger
Cu-1.15at%Cr-0.03at%Zr-0.14at%Si was irradiated with 300 keV Cu+ ions to damage levels between 0.01 and 20 dpa at displacement rates of 2.3 × 10-5 to 2.3 × 10-2 dpa/s and temperatures of 80 to 883 K. The effect of heavy ion irradiation on the stability of the coherent chromium phase in this alloy was examined using transmission electron microscopy (TEM). The precipitates were observed to shrink at 80 K and at room temperature as well as at 803 K according to the square root of the fluence. After 0.1 dpa the strain contrast of the coherent chromium precipitates disappeared completely at 80 K as well as at room temperature. © 1992.
Stress response behaviour of and microstructural evolution in Nimonic PE16 LCF tested at temperatures up to 923 K
(2000) M. Sundararaman; V. Singh; W. Chen; R.P. Wahi
The cyclic stress strain behaviour of nickel base superalloy, Nimonic PE16 has been studied at a constant strain rate of 4 × 10-3s-1 at different strain amplitudes as a function of γ′ particle size for temperatures up to 650°C. Fatigue softening after initial hardening was observed in all samples containing γ′ particles up to an average size of 30 nm tested at room temperature while a saturation in the cyclic stress response behaviour after initial hardening was observed in samples containing γ′ particles above an average size of 21 nm tested at 650°C. Detailed TEM investigation was carried out to understand the observed fatigue behaviour. Fatigue softening was noticed to be associated with shearing of γ′ particles and localisation of slip while saturation behaviour was associated with Orowan looping and non-localisation of slip. Particle size at which the mechanism of deformation changes from shearing to looping decreases with increase of test temperature. This behaviour is explained on the basis of the effect of test temperature on the line tension of dislocations. In the case of shearable precipitates, width of deformation band decreases with increase of temperature reaching that of single slip lines at 923 K. Change of deformation microstructure with testing temperature, γ′ free bands at room temperature, fine γ′' particles within the bands at 673 K and sheared γ′ at 923 K, are explained on the basis of combined effect of mechanical shearing and fatigue enhanced diffusion within bands. Fatigue life decreases with increase of test temperature.