P. Rodriguez

Bio: P. Rodriguez is an academic researcher from Indira Gandhi Centre for Atomic Research. The author has contributed to research in topics: Corrosion & Stress corrosion cracking. The author has an hindex of 9, co-authored 15 publications receiving 646 citations.

Serrated plastic flow

Abstract: This paper attempts an assessment of the current understanding of the phenomenon of “serrated plastic flow”, which manifests itself as serrations, load drops, jerkiness or other discontinuities in the stress-strain curves obtained in constant extension rate tensile tests, and as sudden bursts of strain in constant loading rate tests and in constant load (stress) creep tests (the so called staircase creep). Though one can identify at least seven physical processes that can cause serrations, the discussion here is restricted mainly to serrated yielding in tension tests originating from dynamic strain ageing (dsa). The characteristics of the five types of serrations that have been identified so far and the experimental conditions under which they occur are discussed. The various models of serrated flow that have been put forward are reviewed critically. Some recent results on 316 stainless steel are presented to illustrate the effects of grain size, temperature and strain rate on serrated flow. Manifestations ofdsa other than serrations such as a negative strain rate sensitivity, positive temperature dependence for flow stress and work hardening, and the ductility minimum are also discussed. Finally the various issues to be resolved are enumerated.

Effect of ferrite transformation on the tensile and stress corrosion properties of type 316 L stainless steel weld metal thermally aged at 873 K

Abstract: This article deals with the effect of the microstructural changes, due to transformation of delta ferrite, on the associated variations that take place in the tensile and stress corrosion properties of type 316 L stainless steel weld deposits when subjected to postweld heat treatment at 873 K for prolonged periods (up to 2000 hours). On aging for short durations (up to 20 hours), carbide/ carbonitride was the dominant transformation product, whereas sigma phase was dominant at longer aging times. The changes in the tensile and stress corrosion behavior of the aged weld metal have been attributed to the two competitive processes of matrix softening and hardening. Yield strength (YS) was found to depend predominantly on matrix softening only, while sig-nificant changes in the ultimate tensile strength (UTS) and the work-hardening exponent, n, occurred due to matrix hardening. Ductility and stress corrosion properties were considerably affected by both factors. Fractographic observations on the weld metal tested for stress-corrosion cracking (SCC) indicated a combination of transgranular cracking of the austenite and interface cracking.

Studies on the influence of metallurgical variables on the stress corrosion behavior of AISI 304 stainless steel in sodium chloride solution using the fracture mechanics approach

Abstract: Stress corrosion data on a nuclear grade AISI type 304 stainless steel in a boiling solution of 5M NaCl+ 0.15M Na2SO4+ 3 mL/L HC1 (bp 381 K) for various metallurgical conditions of the steel are presented in this article. The metallurgical conditions used are solution annealing, sensitization, 10 pct cold work, 20 pct cold work, solution annealing + sensitization, 10 pct cold work + sensi-tization, and 20 pct cold work + sensitization. The fracture mechanics approach has been used to obtain quantitative data on the stress corrosion crack growth rates. The stress intensity factor,K 1, andJ integral,J 1, have been used as evaluation parameters. The crack growth rates have been measured using compact tension type samples under both increasing and decreasing stress intensity factors. A crack growth rate of 5 X 10-11 m/s was chosen for the determination of threshold para-meters. Results of the optical microscopic and fractographic examinations are presented. Acoustic signals were recorded during crack growth. Data generated from acoustic emissions, activation energy measurements, and fractographic features indicate hydrogen embrittlement as the possible mechanism of cracking.

Radiation effects in nuclear reactor materials—correlation with structure

Abstract: A review of radiation effects in nuclear reactor materials has been made; the irradiation effects have been correlated with the crystal structure of the materials. Five phenomena, irradiation hardening, irradiation embrittlement, irradiation creep, irradiation growth and void swelling that occur in materials by neutron irradiation in a reactor environment have been discussed with a view to explaining the physics of the phenomena and the engineering consequences. Metallurgical approaches for improving the irradiation performance of materials and for developing new alloys with better resistance to radiation damage have been pointed out.

Mixed plutonium-uranium carbide fuel in fast breeder test reactor

Abstract: This paper describes the development of the indigenous plutonium-uranium mixed carbide nuclear fuel for the fast breeder test reactor. The fuel has performed satisfactorily and produced, for the first time in our country, nuclear electricity from a fast reactor. The experience and knowledge gained in the fuel development has provided great confidence for undertaking a programme on utilization of fast reactor technology for power production.

Strain rate effects in the ultrafine grain and nanocrystalline regimes—influence on some constitutive responses

Abstract: Mounting evidence is pointing to some emerging novel behaviors of metals with ultrafine-grain (UFG) and/or nanocrystalline (NC) microstructures. One such novel behavior is related to the thermodynamic and kinetic aspects of plastic response in the UFG/NC regime. Two inter-related parameters, viz., the strain rate sensitivity (SRS) and the activation volumes of plastic deformation, are used as fingerprints for the thermodynamics and kinetics of plastic deformation. Changes of these parameters with grain size may indicate transition of plastic deformation mechanisms. Therefore, investigations of these phenomena may bring out new strategies for ingenious design and synthesis of UFG/NC materials with desirable properties. In this article, we present a critical review on the experimental results and theories associated with the SRS of UFG/NC metals with different lattice structures, and the influences on some constitutive responses.

Microstructural and mechanical influences on dynamic strain aging phenomena

Abstract: The Portevin-Le Chatelier (PLC) effect is a manifestation of macroscopic scale non-uniformities which have their origins on a microstructural level. The coordination of dislocation level events wit...