Materials Science Forum Vols. 830-831

Abstract: Owing to high elastic modulus and good strength, copper beryllium alloys are widely used in many engineering applications. The addition of beryllium to copper makes the alloy respond to aging treatment and thus develops very high strength. Conventional heat treatment cycles are available for copper-beryllium to obtain peak ageing hardness condition. Present study has focused on developing a heat treatment cycle to obtain synergetic combination of moderate strength and good toughness for the C17200 copper-beryllium alloy. Ageing curves have been generated for varying temperature and time. Detailed mechanical properties (hardness, impact, tensile) evaluation at room temperature and sub-zero temperatures have been carried out for the selected samples. Modified heat treatment cycle resulted in higher toughness with adequate strength. Optical microscope (OM) and transmission electron microscope (TEM) analysis were carried out to understand the precipitation behavior. Also, measurements of coefficient of thermal expansion (CTE) and thermal conductivity were carried out on the aged samples.

Abstract: Quench heat treatment consists of rapid cooling of steel alloys after austenetization by subjecting them to cooling in a suitable cooling medium. At the heart of quench treatment is the transient heat transfer that occurs between the metal surface and the quenchant at their interface. This governs the quality of the component as it influences phase transformation, residual quench stresses and mechanical properties developed. In the present research work, spatially dependent transient heat flux in the axial direction was estimated using cooling curve analyses coupled with inverse heat conduction technique. A standard Inconel 600 probe instrumented with multiple thermocouples and heated to 865°C was quenched in distilled water (DW) and DW based multi walled carbon nanotubes (MWCNT) quench media. For evaluating the cooling performance, nanoquenchants with concentrations of 0.01, 0.1 and 1.0g/lt. were prepared. The cooling rate curve calculated from the measured temperature at the geometric center of the probe and the estimation of spatially dependent heat fluxes showed that the heat extraction during quenching with MWCNT nanoquenchant (0.1g/lt.) was higher than the other quenchants. The measured values of thermal conductivity and viscosities of quenchants did not show any significant variation.

Abstract: – Mg-3Al-1Zn (AZ31) alloy was caliber rolled isothermally at the temperature of 300 °C to develop fine grains of 3.6 μm. Annealing was carried out at various times and temperatures. Along with microstructure, annealing affects the hardness and hardness penetration depth. The hardness penetration depth of caliber rolled bar during annealing at 300 to 450 °C was investigated for 5 to 60 minutes. The change in hardness penetration depth were analysed and the mechanisms involved were discussed.

Abstract: Precipitation hardening stainless steel (17-4-PH) of 3 mm thick sheet was welded by gas tungsten arc welding (GTAW) process using a matching composition filler wire of ER 630. The welds were subjected to various post weld heat treatment (PWHT) cycles viz., H900, H1025 and H1150. Tensile properties (UTS, 0.2% YS, and % EL.), hardness survey across the weld and detailed optical microscopy have been carried-out on as-welded and after different PWHT conditions samples. Results showed that H900 heat treatment condition attained higher mechanical properties than H1025 and H1150.

Abstract: Gimbaling the engine nozzle within a specified angle through hydraulic actuator modules is commonly used to control the trajectory path of satellite launch vehicles. During one of the hot test of a liquid engine stage, a drop in system pressure in actuator module was noticed due to cracking of case drain plumbing inside the ferrule. The tensile and fatigue (axial and bending) test of the tube material was carried out to understand the cause of failure, simulating the actual service conditions such as strength and bending moment in assembled tube. Findings of the metallurgical investigation along with the fatigue test results were presented in this paper.

Abstract: Conventional tensile test methods are used for service exposed high temperature boiler tubes to evaluate the deterioration in mechanical properties such as tensile strength, yield strength and percentage elongation. The mechanical properties are required to be evaluated periodically as the boiler components undergo material degradation due to aging phenomena. The aging phenomena occurs due to continuous exposure of tubes to high temperature & pressure steam prevailing inside the tubes and high temperature exposure to corrosive combustible gases from the external surfaces within the boiler.A recent developed new technique called small punch testing has been used to evaluate the tensile properties of SA 213T22 grade steel predominantly exists in super-heater and re-heater sections of boiler. The small punch tests have been carried out on the miniature disk shaped specimens of diameter of 8.0 mm and 0.5 mm thickness extracted from both the new and service exposed tubes. Conventional uniaxial tensile tests on standard specimens from the same tube material have also been performed for comparison. The service exposed tubes showed considerable loss in mechanical properties in both the conventional and small punch test results. Correlations of tensile properties have been obtained based on the comparative analysis of both small punch and uniaxial tensile test results. Further, the study showed that an appropriate empirical relation could be generated for new and service exposed materials between both the techniques. Conventional test methods require large quantity of material removal for test samples from in-service components whereas small punch test method needs only a miniature sample extraction. This small punch test technique could also be extended to evaluate the thicker section boiler components such as pipelines and headers in the boiler as a part of remaining life assessment study. Also this technique could be a useful tool to any metallic component where large quantity of sample removal may be difficult or may not be feasible.

Abstract: Elastic constants are the fundamental key parameters in the mechanical behaviour of engineering materials under stressed condition. This paper explains the determination of elastic constants of commercially pure titanium (Grade-2) at ambient temperature using three independent test methods including quasi-static tensile test with strain gauged specimen, ultrasonic pulse echo method and resonance based impulse excitation technique. The results are statistically analysed and compared.

Abstract: Advanced Ultra Super-Critical (AUSC) power plants are envisaged for achieving higher thermodynamic efficiency by operating at temperatures and pressures of 710/720 °C and 310 ata, respectively which are significantly higher than sub-critical (conventional) and supercritical power plants. This has led to tremendous research in selection of new and advanced materials to meet high temperature requirements. Ni-base superalloys having known to have excellent creep-rupture behavior were selected for high temperature sections of boiler while austenitic stainless steels were selected for moderately high temperature sections considering the economical feasibility. Since both these materials have to be fabricated for application in boiler tubes, dissimilar metal welding is inevitable. This work discusses creep-rupture evaluation of one such case of dissimilar welds, i.e., between Inconel 617 (IN 617) and SUS 304H. IN 617 is a Ni-base superalloy while SUS 304H is a Cu-precipitated austenitic stainless steel. Welding was carried out using IN 617 filler material for producing defect free welds. Creep-rupture samples were prepared incorporating the complete cross-weldment for understanding mechanical behavior as a result of prolonged exposure to elevated temperature and stresses. Creep-rupture testing was carried out at 600, 650 and 700°C at suitable stresses to obtain rupture times in the excess of 3000 hours in a few test conditions. Detailed characterization studies when carried out on ruptured samples revealed the weakest zone to be heat affected zone towards SUS 304H which led to failure. This work also provides insight into the possible creep-mechanisms that operate in various zones of weldments. Phases formed as a result of exposure to stress and temperature for a prolonged duration are also discussed. Comparison of the data obtained with data available in literature was carried out and performance of weldments was analyzed and reported.

Abstract: Elastic constants are the fundamental key parameters to understand the mechanical behaviour of engineering materials under stressed condition. This paper explains the test methodology and provides results of experiments carried out using resonance based high temperature impulse excitation technique test facility for the measurement of technical elastic moduli i.e., Young’s modulus (E), Shear modulus (G), Poisson’s ratio (ν) and internal friction (Q^-1) of two nickel-base polycrystalline super alloys IN718 and Haynes 214 from ambient to 650°C temperature in argon environment during heating and cooling.

Abstract: Ti-6Al-4V alloy is widely used in Aerospace applications owing to its high specific strength, low coefficient of thermal expansion and good corrosion resistance. Presence of interstitial elements in the alloy has some significant effects on its properties. However the poor notch toughness and cryogenic ductility restricts the usage of Ti-6Al-4V for temperatures lower than 77 K (-196 °C). The Extra Lower Interstitial grade alloy was developed in order to improve the notch toughness and cryogenic ductility of the Ti-6Al-4V alloy. In this refined grade, the interstitials, Oxygen and Carbon are controlled to a maximum limit of 0.12% and 0.08% respectively as compared to a maximum of 0.2% and 0.1% of standard Ti-6Al-4V alloy. In this study, the ELI grade of Ti-6Al-4V rods from three different manufacturing sources were subjected to tensile test at liquid hydrogen temperature at 20 K (-253 oC). The tensile properties obtained are compared and analyzed. The obtained ductility at 20 K is observed to have close relation with the chemical composition and interstitial content and compared with the Ti5Al2.5Sn-ELI which is ideally suitable for low temperatures upto 20 K, owing to its single phase HCP structure. A correlation has been made between the ductile properties and microstructure. By close control of chemical composition and mechanical working, Ti6Al4V-ELI can be used for temperatures lower than 77 K (-196 oC), which is otherwise is forbidden. This paper details the test data obtained from three different compositions of Ti6Al4V-ELI at 20 K, which enables the usage of this material for temperatures lower than 77 K (-196 °C) upto 20 K.