T. K. Sahoo

Effect of Microstructural Variation on Erosion Wear Behavior of Ti-6Al-4V Alloy

The present article describes the effect of microstructural variations—that is, lamellar, bimodal, and equiaxed—on solid particle erosion wear behavior of Ti-6AL-4V alloy at room temperature. Erosion tests were carried out at various test conditions using an air jet–type test rig and Taguchis orthogonal array experimental design. The results indicated that impact velocity is the most significant controlling factor influencing the solid particle erosion wear of Ti-6Al-4V alloy followed by impact angle, microstructural variation, and size of erodent. The lamellar microstructure of Ti-6Al-4V alloy has excellent erosion resistance, followed by bimodal and equiaxed microstructures. Ploughing or pile-up leading to platelet formation was found to be the primary mechanism of material loss in erosion of Ti-6Al-4V alloy. This mechanism of material loss is independent of its microstructural variation. These results were determined after observation of the eroded surface under a scanning electron microscope. Optical microscopy, Rockwell hardness testing, and scanning electron microscopy were used to characterize the microstructures and eroded surfaces of the Ti-6Al-4V alloy in order to correlate the results obtained.

Effect of primary alpha phase variation on mechanical behaviour of Ti–6Al–4V alloy

Abstract Small punch tests (SPTs) have been carried out at room temperature to correlate the microstructural variation of Ti–6Al–4V alloy with that of SPT parameters. Microstructural variation in terms of different volume fractions of primary alpha phase of Ti–6Al–4V alloy has been introduced as a result of solution annealing at different temperatures followed by thermal aging. Small punch test parameters, i.e. total area under the load vs displacement curve, area under the zone of elastic bending, plastic bending and plastic instability have been found to increase from the content of 10% primary alpha phase to 20% primary alpha phase and then these are decreasing from the content of 20% primary alpha phase to 30% primary alpha phase.

Effect of Microstructural Degradation on Solid Particle Erosion Behavior of 2.25Cr-1Mo Steel

The present article evaluates the influence of independent control factors such as microstructural degradation, impact velocity, impingement angle, and erodent size on solid particle erosion behavior of 2.25Cr-1Mo steel using a statistical approach. Microstructural degradation in this steel has been introduced as a result of thermal aging corresponding to Larson-Miller parameter (LMP) values of 33,012, 35,402, 37,846, and 38,374. Solid particle erosion tests were carried out using a sand blast–type test rig following a well-planned experimental schedule based on Taguchis orthogonal arrays. The erosion rate of this steel decreases with increase in the severity of thermal aging. This observed phenomenon could possibly be attributed to spheroidization of lenticular-shaped carbides to globular-shaped carbides as a result of increase in the severity of thermal aging. With the help of signal-to-noise ratios and analysis of variance (ANOVA), an optimal combination of control factors to minimize the solid particle erosion behavior of 2.25Cr-1Mo steel was determined. Among all four control factors, the LMP representing the extent of thermal aging is the most significant control factor influencing the solid particle erosion behavior of this steel, followed by impingement angle, impact velocity, and size of erodent. Results indicated that the LMP has a greater static influence of 46.33%, impingement angle has an influence of 42.51%, impact velocity has an influence of 7.47%, and size of erodent has an influence of 1.13% on solid particle erosion of this steel. Material loss during solid particle erosion of 2.25Cr-1Mo steel is found to be ductile in nature and primarily controlled by cutting and ploughing action.

Experimental Study on the Effect of Microstructure on Dry Sliding Wear Behavior of Titanium Alloy Using Taguchi Experimental Design

The present article depicts the influence of independent control factors such as microstructural variation, normal load, sliding velocity, and test duration on the dry sliding wear behavior of titanium alloy at room temperature using a statistical approach. Different heat treatments were carried out in a controlled manner to produce various microstructural features (i.e., lamellar, bimodal, and equiaxed) in this alloy. A lamellar microstructure is found to be harder than bimodal microstructure followed by an equiaxed microstructure in this alloy. Dry sliding wear tests were carried out using a multiple tribotester following a well-planned experimental schedule based on Taguchis orthogonal arrays. The dry sliding wear behavior of this alloy consisting of various microstructural features is related to their hardness values. The results indicated that a lamellar microstructure has the lowest sliding wear resistance followed by bimodal and equiaxed microstructures. Using signal-to-noise ratios and analysis of variance (ANOVA), an optimal combination of control factors that minimize the dry sliding wear in this alloy were determined. Among all four control factors, normal load is the most significant control factor influencing the dry sliding wear behavior of the investigated titanium alloy, followed by microstructural variation, sliding velocity, and test duration. Normal load has a greater static influence of 39.53%, microstructural variation has an influence of 31.55%, sliding velocity has an influence of 21.6%, and test duration has an influence of 5.7% on the dry sliding wear of this alloy. Two wear mechanisms were identified: oxidative wear occurs at the lowest sliding velocity and delamination wear occurs at the highest sliding velocity. Optical microscopy, scanning electron microscopy, and Rockwell hardness measurements were used to characterize the microstructures in order to correlate the results obtained.

Effect of Volume Fraction of Primary Alpha Phase on Solid Particle Erosion Behavior of Ti-6Al-4V Alloy

The present article evaluates the influence of independent control factors such as percentage of primary alpha phase, impact velocity, impingement angle, and erodent size on solid particle erosion behavior of Ti-6Al-4V alloy using a statistical approach. Microstructural variation in terms of different percentage of primary alpha phase of investigated alloy has been introduced by solution annealing it at different temperatures followed by thermal aging. Solid particle erosion tests have been carried out using a sand blast–type test rig following an experimental schedule based on Taguchis orthogonal arrays. It is observed that erosion rate and the value of percentage elongation decreased with an increase in the content of primary alpha phase from 10 to 20% and then increased for the value corresponding to the content of 30% primary alpha phase in this alloy. We observed that the solid particle erosion behavior of the investigated alloy consisting of various percentages of primary alpha phase is related to their ductility. Among all four control factors, impact velocity of the erodent has been found to be the most significant control factor influencing the solid particle erosion behavior of this alloy followed by impingement angle, percentage of primary alpha phase, and erodent size. Impact velocity has greatest static influence of 91.35%, impingement angle has an influence of 4.69%, percentage of primary alpha phase has an influence of 2.28%, and erodent size has an influence of 0.42% on solid particle erosion having R2 = 0.99. Material loss during solid particle erosion of this alloy was found to be ductile in nature. Ploughing or pile-up leading to platelet formation is the primary mechanism of material loss during erosion of the alloy.

Acoustic emission study of deformation behaviour of sensitised 304 stainless steel

Abstract A systematic study has been undertaken to correlate the changes in acoustic emissions during tensile deformation of sensitised AISI type 304 stainless steel. Samples of a typical 304 stainless steel were sensitised at 700°C for 4, 14 and 24 h after being austenised at 1050°C for 30 min. AE signals were recorded during tensile test by using two sensors with 125 kHz resonant frequency. The results showed significant change in generation of AE during tensile deformation of sensitised AISI 304 stainless steel in compare to solution annealed material. This type of behaviour could be attributed to the microstructural changes in the sensitised specimens especially formation of continuous Cr23C6 carbides on grain boundaries which lead to increase in shearing by dislocations.

Experimental study on microstructural variation in near alpha titanium alloy during non-optimal regime of superplastic deformation

Abstract Superplasticity is generally achieved in titanium alloys with a fine grained microstructure when deformation is carried out under narrow ranges of strain rate and temperature. Under these conditions, titanium alloys show large elongation with a relatively stable microstructure. When the aforesaid conditions lie beyond a certain limit during deformation process, non-optimal process of superplastic deformation is observed. The microstructure changes actively during the non-optimal process of superplastic deformation. Near alpha titanium alloy has been used in the present study to find out those parameters of microstructure, which are varying significantly during non-optimal process of superplastic deformation. Superplasticity tests have been carried out at 930°C with constant strain rates of 1×10−4 and 5×10−4 s−1 and jump wise varying strain rates between 1×10−4 and 5×10−4 s−1. Results indicated that microstructural parameters, i.e. percentage of alpha phase, number of alpha grains per unit area, average size of alpha grain, parameter of non-uniaxiality of alpha grain and grain boundary area of alpha grain, varied significantly during non-optimal process of superplastic deformation. Strain induced grain growth and deformation induced phase transformation are also observed in near alpha titanium alloy during non-optimal process of superplastic deformation. Optical microscope, micro-Vickers hardness test and X-ray diffraction have been used to characterise the microstructure of the near alpha titanium alloy.

Microstructural characterisation of thermally degraded 2·25Cr–1Mo steel using ultrasonic measurement and its correlation with mechanical properties

Abstract Ultrasonic testing is a sensitive tool not only for defect detection and evaluation of components and structures but also to characterise microstructural features which affect mechanical properties. In this study, four different thermally degraded specimens of 2·25Cr–1Mo steel have been prepared by aging at 873 K for 10 h, 923 K for 20 h, 973 K for 40 h and 973K for 80 h to obtain variation in microstructural features. Mechanical properties of each specimen having different microstructures were investigated using tensile and hardness tests. Ultrasonic parameters of each specimen having different microstructural features were studied by pulse echo technique using 5 MHz longitudinal probe. It has been observed that ultrasonic velocity and attenuation both increased with increase in the size of carbide precipitates obtained due to increased time and temperature of aging. Our results indicated that these ultrasonic parameters could be used as a tool to assess the degraded microstructure of operating components in service.

Effect of Microstructure on the Creep Properties of Ti–6Al–4V Alloys: An Analysis

The effects of microstructure types and microstructural parameters on creep properties were investigated systematically through an analysis of microstructure and creep properties of Ti–6Al–4V alloys based on the available literature data. The results indicated that the creep properties of the Ti–6Al–4V alloy are strongly dependent on microstructure type. Creep resistance of Ti–6Al–4V alloys is better in lamellar microstructure followed by bimodal and equiaxed microstructure respectively. Also, microstructural parameters such as the size of both prior beta grain and alpha colony and thickness of alpha lamellae in the lamellar microstructure, the volume fraction of primary alpha phase in bimodal microstructure and size of alpha phase in equiaxed microstructure can influence the creep properties.