http://202.88.229.59:8080/xmlui/handle/123456789/222 Tue, 14 Apr 2026 19:50:50 GMT 2026-04-14T19:50:50Z http://202.88.229.59:8080/xmlui/handle/123456789/379 Thermomechanical Fatigue Behaviour of a Modified 9Cr-1Mo Ferritic Steel Mathew, M D; Nagesha, A; Kannan, R; Sandhya, R; Sastry, G V S; Rao, K Bhanu Sankara; Singh, Vakil Thermomechanical fatigue (TMF) tests were carried out on a modified 9Cr-1Mo ferritic steel (P91) under a mechanical strain control mode using a strain amplitude of ±0.4% and a strain rate of 1.2×10−4 s−1. In-Phase (IP) and Out-of-Phase (OP) strain-time waveforms were employed for the tests which were performed under different temperature ranges in the interval, 573-923 K. For the sake of comparison, isothermal LCF (designated as IF) tests were also carried out at the maximum temperatures (Tmax) of TMF cycles on similar specimens and using the same strain amplitude and strain rate. Isothermal cycling was observed to be the most detrimental while IP TMF yielded the highest lives. However, with an increase in the Tmax of TMF cycling, the difference in lives was seen to narrow down. Also, lives under IP TMF and IF cycling were seen to reduce more drastically compared to OP cycling on account of a greater creep damage accumulation. A continuous cyclic softening characterized the stress response of the alloy under all testing conditions. The lower lives observed under OP cycling were rationalised in terms of oxidation damage and mean stress development. The observed behaviour was explained on the basis of detailed TEM investigations. Tue, 01 Jan 2013 00:00:00 GMT http://202.88.229.59:8080/xmlui/handle/123456789/379 2013-01-01T00:00:00Z http://202.88.229.59:8080/xmlui/handle/123456789/378 Modelling the Effect of Grain Boundary Sliding on Creep Lifetime: Application to Two Austenitic Stainless Steel Mathew, M D; Mahesh, Sivasambu A model capable of representing the evolution rate of various damage mechanisms pertinent to creep rupture of austenitic stainless steels is utilized to study the role of grain boundary sliding on the damage evolution in the form of cavitational damage at grain boundary facets and wedge cracking at triple lines and on the creep lifetime of a standard creep specimen. Reduced grain boundary sliding reduces the rate of damage evolution and hence prolongs creep lifetime at higher stresses. However, creep lifetime at lower stresses is controlled by diffusional cavitation and remains unaffected by grain boundary sliding. Tue, 01 Jan 2013 00:00:00 GMT http://202.88.229.59:8080/xmlui/handle/123456789/378 2013-01-01T00:00:00Z http://202.88.229.59:8080/xmlui/handle/123456789/377 Microstructural Modifications due to Tungsten and Tantalum in 9Cr Reduced Activation Ferritic Martensitic Steels on Creep Exposure Mathew, M D; Mythili, R; Ravikirana; Vsnaja, J; Laha, K; Saroja, S; Jayakumar, T; Rajendrakumar, E Replacement of Mo and Nb by W and Ta in modified 9Cr-1Mo class of steels has been significantly useful for achieving reduced activity and improved mechanical properties. The addition of W and Ta strongly influences microstructure which comprises of the substructural changes and precipitation kinetics under both thermal and stress exposure. This study focusses on the effect of W and Ta on microstructural changes on thermal and creep exposure at 823K in 9Cr-W-Ta-0.2V- 0.1C steels, with W and Ta concentrations varying from 1 to 2% and 0.06 to 0.14% respectively. Increase in W from 1 to 1.4 or 2%, was beneficial to retain lath structure and retard the coarsening of M23C6 during long term thermal aging. Detailed microstructural investigation of the steesl after creep deformation showed extensive subgrain formation and coarsening of M23C6 carbides than just thermal exposure. Influence of W on subgrain size was more pronounced than Ta. Increase in W was found to be useful to control the coarsening rate of M23C6 carbides, even under stress, while MX precipitate size showed no significant change. Tue, 01 Jan 2013 00:00:00 GMT http://202.88.229.59:8080/xmlui/handle/123456789/377 2013-01-01T00:00:00Z http://202.88.229.59:8080/xmlui/handle/123456789/376 Improvement in Creep Damage Tolerance of 14Cr-15Ni- Ti modified Stainless Steel by Addition of Minor Elements Mathew, M D; Latha, S; Panneer Selvi, S; Mannan, S L Creep properties of 14Cr-15Ni-Ti modified steel, alloyed with phosphorus and silicon were investigated at 973 K in the stress range 175-250 MPa. The phosphorus content in the alloys was 0.025 and 0.04 wt.%, silicon 0.75 and 0.95 wt.% and titanium in the range 0.16-0.3wt.%. The variation between minimum creep rate and rupture life for these alloys was found to follow the Modified Monkman Grant relationship. The inverse of Modified Monkman Grant relationship which is defined as the damage tolerance parameter was found to be above ten for these alloys, indicating that these alloys can withstand high strain concentrations. Optical microscopic investigations revealed extensive matrix deformation and precipitation. Creep damage in the form of cracks or cavities was not observed in these alloys corroborating high tolerance for creep damage. Addition of boron was found to prevent grain boundary damage. Tue, 01 Jan 2013 00:00:00 GMT http://202.88.229.59:8080/xmlui/handle/123456789/376 2013-01-01T00:00:00Z