Bhanu Pant

On the Prediction of Strength from Hardness for Copper Alloys

Hardness and strength values of over 55 copper alloys strengthened by solid solution strengthening, precipitation hardening, cold working, and dispersion strengthening were compiled. The yield strength (YS) and ultimate tensile strength (UTS) values of the copper alloys examined ranged between 50 to 1300 MPa and 200 to 1400 MPa, respectively. The compiled values were classified based on strain-hardening potential an indirect method to understand the effect of strain-hardening characteristics. Least squares regression analysis was employed to establish correlations between strength and Vickers hardness values. Strain-hardening potential showed a significant effect on the correlations. In all the cases, a linear relation was obtained for both YS and UTS with hardness for the entire range of values under analysis. Simple empirical equations were proposed to estimate the strength using bulk hardness. The proposed correlations obtained for the entire range of values were verified with experimental values. A good agreement was observed between experimental and predicted values.

Properties and Strengthening Mechanisms in Cold-Rolled and Aged Cu–3Ag–0.5Zr Alloy

In the present study, the yield strength of 80% cold-rolled and aged Cu–3Ag–0.5Zr alloy was theoretically estimated for five strengthening mechanisms using data obtained from optical microscopy and transmission electron microscopy. For comparison, the mechanical properties were evaluated in different conditions. The theoretical yield strength was in good agreement with the experimental value. The major contribution to yield strength in cold-rolled and aged condition was from coherency strengthening and dislocation strengthening.

Effect of Simulated Brazing Cycle on the Microstructure and Mechanical Properties of Cu-Cr-Zr-Ti Alloy

Cu-Cr-Zr-Ti alloys are widely used for fabrication of thrust chamber in liquid rocket engines, because of their high thermal conductivity and adequate strength. The alloy should be used in peak-aged condition to achieve the best combination of strength and conductivity. However, realization of final component involves forming and brazing operations which limit the usage of the alloy in peak aged condition. Therefore, an attempt has been made to study the effect of the simulated brazing treatment on the microstructure and mechanical properties using optical microscopy, electron microscopy, mechanical testing and hardness measurement. The high temperature brazing treatments resulted in tremendous grain growth. The measured hardness is observed to be in line with the grain size of the specimens. The hardness and tensile strength decreased in samples subjected to simulated brazing cycle, implying requirement for a post braze treatment. After the post brazing treatment the optimum mechanical properties have been achieved at room temperature. Low ductility was observed at 600°C in the samples subjected to simulated brazing cycle.

Age-Hardening Characteristics of Cu-3Ag-0.5Zr Alloy

Among the copper alloys, the Cu-3Ag-0.5Zr alloy is one of the potential candidates for combustion chamber of liquid rocket engine because of its optimum combination of high strength with thermal conductivity. The present study is a detailed characterization of microstructure, strength, and electrical conductivity during the aging treatment. The aging cycle for Cu-3Ag-0.5Zr alloy after the solution treatment (ST) was optimized to obtain higher hardness without compromising on electrical conductivity. The precipitates responsible for strengthening in aged samples are identified as nanocrystalline Ag precipitates with an average diameter of 9.0±2.0 nm.

Thermal Conductivity of Cu-Cr-Zr-Ti Alloy in the Temperature Range of 300-873K

In the present investigation, thermal conductivity of Cu-Cr-Zr-Ti alloy was determined as the product of the specific heat (Cp), thermal diffusivity (α), and density (ρ) in the temperature range of 300‐873K. The experimental results showed that the thermal conductivity of the alloy increased with increase in temperature up to 873K and the data was accurately modeled by a linear equation. For comparison, thermal conductivity was also evaluated for OFHC copper in the same temperature range. The results obtained were discussed using electrical conductivity and hardness measurements made at room temperature. Transmission electron microscopy (TEM) was done to understand the microstructural changes occurring in the sample after the test. Wiedemann-Franz-Lorenz law was employed for calculating electronic and phonon thermal conductivity using electrical conductivity. On the basis of studies conducted it was deduced that in situ aging may be one of the reasons for the increase in thermal conductivity with temperature for Cu-Cr-Zr-Ti alloy.

Effect of Pressure and Temperature on Phase Transformation and Properties of Titanium Aluminide Obtained through Reaction Synthesis

Reaction synthesis process has been used to develop γ titanium aluminide using elemental powders. Powder mixture of Ti-48 at. pct Al was prepared in ball mill and reaction synthesis was carried out in hot press with varying temperature and pressure. Titanium aluminide synthesized under high pressure and temperature resulted in better properties with respect to densification, homogenization response, mechanical properties and oxidation resistance as compared to that synthesized under low pressure and temperature. Al rich phases were observed in as-synthesized condition in all the experiments. However, some Ti rich phases were also found in high pressure-temperature synthesized samples. Density, hardness and tensile strength have been correlated with applied pressure through empirical relations. Variation in density with pressure is found to be logarithmic whereas hardness and tensile strength variation with pressure is polynomial.

Closed Die Hammer Forging of Inconel 718

A method for the production of Inconel 718 (IN-718) hemispherical domes by closed die hammer forging is proposed. Different combination of operations employed for production are as follows: (i) preforging

Heat Treatment and Thermo-Mechanical Treatment to Modify Carbide Banding in AISI 440C Steel: A Case Study

In the present case study, simple heat treatment and thermo-mechanical treatment (TMT) are suggested to salvage AISI 440C steel bars with carbide banding. Optical microscopy, scanning electron microscopy, and hardness measurement were employed to characterize the steel before and after treatments. The experimental results indicate that carbide refinement and uniform distribution of carbides can be achieved by TMT. The hardness of the steel after TMT was higher than 58 HRC in hardened (H1050), cryo-treated (C-80), and tempered (T180) conditions. This TMT cycle was implemented to produce one batch of rings free of carbide banding for outer race of ball bearings.

Effect of Welding Processes (GTAW & EBW) and Solutionizing Temperature on Microfissuring Tendency in Inconel 718 Welds

Inconel 718 is widely used superalloy in the Indian space program for high temperature application. Some of the newer applications envisage use of this alloy in very critical high pressure oxygen carrying vessels. The alloy is frequently used in welded condition which requires extensive characterization of various types of welds viz Electron beam welding (EBW) and Gas tungsten arc welding (GTAW). In many cases the weldability of Inconel 718 is found to be limited by microfissuring phenomenon in the weld heat affected zone. Microfissures are fine intergranular cracks and their severity strongly depends on pre-weld solution treatment temperature (grain size), weld heat input and concentration of impurities (B, P and S) in the base metal. In the present work, a study was undertaken to compare the microfissuring tendency in EBW and GTAW processes using two pre-weld solution treatment temperatures. The samples were solution treated at 970°C and 1050°C to generate different grain sizes. Amount of heat input and cooling rate were calculated since they are known to affect the microfissuring and an effort was made to understand their role on the microfissuring. It was observed that microfissuring susceptibility is more at coarser grain size. Severity is more in EBW. The reasons for this phenomenon have been discussed in this paper correlating microfissuring with microstructures and other factors. Procedures to achieve minimal microfissuring during welding have also been brought out.

Reaction Synthesis and Homogenization Of γ + α2 Titanium Aluminide Alloys

Titanium aluminide alloys Ti – 48 at.% with additives of chromium, niobium and boron obtained by reaction synthesis from powder mixtures of the elements and subsequent heat treatment are studied. The alloys are subjected to chemical analysis, density and hardness measurements, light, scanning and transmission electron microscopy, energy dispersive local chemical analysis, and x-ray diffractometry. It is shown that the heat treatment affects positively the synthesis of titanium aluminides.