Standard Heat Treatment Condition Research Articles

Effect of Substrate's Heat Treatment on Microstructure and Mechanical Properties TLP Bonding of Dissimilar X-45/FSX-414 Cobalt Based Superalloys

In this study, a dissimilar joint of cobalt based superalloys X-45 and FSX-414 has been created under the standard heat treatment conditions with the nickel-based BNi-9 interlayer with the thickness of 50 μm by the transient liquid phase bonding process. Solution heat treatment (1150 °C/4 h) was used for bonding and the aging heat treatment (980 °C/4 h) for the homogenization of the bond. Optical metallography, Field Emission Scanning Electron Microscope with Energy Dispersive X-ray Spectroscopy, Differential scanning calorimetry, micro-hardness test and shear strength test were used for the characterization of microstructural and mechanical evolution in base metals and bonds. The solution heat treatment leads to the dissolution of a part of the M23C6 and M6C carbides in the substrate of superalloys, which due to the aging heat treatment secondary and fine carbides M23C6 precipitate in the substrate and help strengthen the superalloys. The diffusion of the boron from the molten interlayer to the base metals resulted in the complete isothermal solidification and a nickel-based single-phase solid solution has been developed. Cobalt-chromium-tungsten-molybdenum-based carboborides precipitation with high hardness in the vicinity of the isothermal solidification zone and in base metals results in the non-homogeneity of microhardness profile along the bonding area. Homogenization heat treatment did not have an effect on the omission of these precipitations, but by more uniform redistribution of the alloying elements strengthen solid solution that could increase shear strength from 655 to 688 MPa, which is somewhat equivalent to the shear strength of the 45-X alloy and also 93% of the shear strength of the FSX-414 alloy.

Study the effect of thermal cycling of brazing and post-brazing processes on Cu-Ni alloy

Analysis of thermal cycling effects of brazing and post-brazing processes is important, which affects the mechanical and metallurgical properties of materials in Standard Heat Treatment condition. The material used for present study is Copper-Nickel alloy, which is to be jointed with Precipitation hardenable (PH) stainless steel. These materials are used in the parts of pre-burner of the Liquid Rocket Engine (LRE). Hardness and microstructure of Cu-Ni alloy was analyzed in Extruded Condition (EC), Brazing Condition (BC) and Post-Braze Condition (PBC). Brazing thermal cycle is done from room temperature (RT) to a temperature of 910 °C with preheating at 500 °C, 600 °C, 700 °C, 850 °C and soaked at 910 °C for 15 min, then furnace cool to 850 °C, after that air cool to room temperature (RT). Post brazing thermal cycle is done at 500 °C for 2hrs to achieve desired properties in base materials and PH stainless steel. Microstructure, mechanical properties at −196 °C, RT, 250 °C, 450 °C & 650 °C were evaluated in PBC, which is essential for design & operation of LRE. Additional Field Emission Scanning Electron Microscope (FE-SEM) investigations prepared with EDS (X-Ray Energy Dispersion Spectrometer) results are used to analyse the fractural failures in detail. The present work discusses about the significant influence of thermal cycling effects on base material properties of brazing and post brazing processes.

Optimization Based on Orthogonal Experiment Design and Numerical Simulation for Carburizing Quenching Process of Helical Gear

Abstract Predictions of distortion and hardness after heat treatment by numerical simulation are very useful for determining the optimum condition and for controlling the distortion of machinery parts. In this article, the combination method of orthogonal experiment and numerical simulation is used to optimize the standard heat treatment condition by reducing the distortion after carburizing quenching. A helical gear made of carburizing steel 20MnCrS5 is simulated using three-dimensional coupled analysis that is based on thermo-mechanical theory. The good agreement between the experiment and simulation is verified by the comparison between the experimental data and the simulated data. Firstly, the influencing factors of distortion after carburizing quenching are investigated and discussed. Four influence factors of heat treatment are selected as follows: carburizing time, the cooling time before 860°C, the holding time at 860°C, and the gear orientation during quenching. Next, selection of the optimal case is then determined by comparing the distortions. Finally, a new optimization method of minimum distortion after carburizing quenching is provided.

Effects of α + β phase deformation on microstructure, fatigue and dwell fatigue behavior of a near alpha titanium alloy

In the present study, a near α titanium alloy, similar to IMI 834 alloy, was melted and thermo-mechanically processed. Different amount of deformation was imparted to the alloy in the α–β region and thereafter tensile, fatigue, and dwell fatigue properties were evaluated in a standard heat treatment condition. Higher α–β deformation resulted into a more refined microstructure. Further, based on EBSD analysis, it was found that higher α–β deformation led to a higher fatigue and dwell fatigue life, along with dwell fatigue life debit as compared to relatively lesser deformed specimen mainly due to hard (0001) basal pole orientations, approximately, parallel to the loading axis.

Brittle fracture of T91 steel in liquid lead–bismuth eutectic alloy

The mechanical behaviour of the T91 martensitic steel has been studied in liquid lead–bismuth eutectic (LBE) and in inert atmosphere. Several conditions were considered to point out the most sensitive embrittling factors. Smooth and notched specimens were employed for respectively monotonic and cyclic loadings.The present investigation showed that T91 appeared in general as a ductile material, and became brittle in the considered conditions only if at least tests were performed in LBE. It turns out that the loading rate appeared as a critical parameter for the occurrence of liquid metal embrittlement of T91 in LBE. For the standard heat treatment condition, loading monotonically the T91 very slowly instead of rapidly in LBE resulted in brittle fracture. Also, under cyclic loading, the crack propagated in a brittle manner in LBE.

Cyclic deformation characteristics and fatigue crack growth behaviour of a newly developed aerospace superalloy Haynes 282

Strain-controlled low cycle fatigue (LCF) and fatigue crack growth (FCG) tests were performed on a newly developed Aerospace superalloy, Haynes 282, in its standard heat treatment condition which consists of a solution heat treatment of 1130°C/2h/water-quench followed by ageing at 1010°C/2h/air-cool and 788°C/8h/air-cool. Cyclic deformation characteristics of the Haynes 282 at room temperature (25°C) were obtained from the LCF test. The LCF test results showed that Haynes 282 experienced a relatively short period of initial cyclic hardening followed by a regime of cyclic softening to specimen failure at all the strain amplitudes employed in the work. Additionally, cyclic deformation parameters determined in the work indicate strong fatigue deformation resistance of the newly developed superalloy. On the other hand, room temperature FCG test results showed that an increase in the stress ratio leads to a rise in the crack growth rate. However, in contrast to common assumption, the loading frequency was observed to have an effect on the crack growth behaviour at room temperature. Furthermore, an increase in temperature from 25°C to 600°C at a testing frequency of 15Hz resulted in an increase in the fatigue crack growth at all stress intensities. However, at a frequency of 0.05Hz, over a relatively large stress intensity range (ΔK), the fatigue crack growth rate decreased with an increase in temperature. The effect of temperature on the fatigue crack growth rate of Haynes 282 are discussed in terms of homogeneity of slip, roughness induced crack closure and dynamic strain ageing.

Transient liquid phase bonding of FSX-414 superalloy at the standard heat treatment condition

Abstract The as-cast samples of FSX-414 Co-based superalloy were heat treated at the standard solution and aging heat treatment cycles. Specimens for joining were cut from the as-cast ingot. Transient liquid phase (TLP) bonding was carried out at the standard solution cycle, using MBF-30 interlayer. Also, bonded specimens were homogenized at the standard aging condition. The microstructure of the as-cast, heat treated and TLP bonded specimens were studied. These studies showed that the non-uniform distributed carbides of the as-cast specimen were replaced by uniform ones during the heat treatment. Eutectic M 23 C 6 carbides were observed in all specimens. Due to the complete isothermal solidification, no eutectic structure was observed in the bond region of bonded specimens. In the diffusion affected zone (DAZ) of these specimens, some intermetallics of the Co B system were seen. Line scan EDS analysis across the bonding zone of the homogenized joint showed more uniform distribution of alloying elements in comparison with the unhomogenized joint. Hardness profiling across the bonding zone showed that isothermal solidification zone's (ISZ) hardness in the homogenized specimen is closer to the base metal (BM) hardness in comparison with the unhomogenized specimen. A hardness peak was observed in the DAZ region of the both homogenized and unhomogenized joints. Shear strength and shear fracture energy of the homogenized joint were about 93% and 82% those of the base metal, respectively. More fibrous zones and smaller dimples were observed at the homogenized joint's fracture surface, in comparison with the unhomogenized one.

Long-Time Thermal Structural Stability Study on NiCr20TiAl Alloy

The coarsening kinetics of main strengthening phase γ′ and the growth behavior of grain boundary carbides have been investigated on NiCr20TiAl alloy aged at 550~750°C for 200~10,000h. The precipitates of NiCr20TiAl alloy at standard heat treatment condition are γ′, M7C3, M23C6 and MC. The coarsening of γ′ precipitates proceeds by Ostwald ripening controlled by volume diffusion in the alloy. Grain boundary carbides M23C6 and M7C3 increase with ageing times and temperatures. The morphologies of precipitates after long-time ageing almost remain the same as that at standard heat treatment condition except 750°C.

Effect of boron on microstructure and mechanical properties of thermomechanically processed near alpha titanium alloy Ti-1100

The effect of 0.2 wt.% of boron on the mechanical properties of Ti-1100, a near α titanium alloy, was evaluated at room temperature and at 600 °C in the as cast and thermomechanically processed (α–β rolled) condition after subjecting it to different heat treatments. Boron addition in Ti-1100 significantly refined the microstructure in the as cast condition but the mechanical properties did not show any improvement. However, in the thermomechanically processed (α–β rolled) and standard heat treatment condition, the yield strength (YS) and ultimate tensile strength (UTS) of the boron containing alloy increased significantly without any drop in elongation-to-failure as compared to the base alloy at both room temperature and 600 °C. No discernible trend was seen in YS and UTS in boron containing alloy with change in solution treatment temperature either at room temperature or at 600 °C.

Microstructural changes during short-cycle heat treatments of cold-work tool steels

Short heat treatment cycles like for induction hardening are rarely investigated on alloyed cold–work tool steels. Therefore little is still known on the microstructural changes during austenitising, quenching and tempering under these conditions. As these investigations show there are significant changes in the alloy distribution depending on the austenitising parameters. Subsequent quenching can lead to high contents of retained austenite. During short cycle tempering the transformation of the tetragonal martensite and the decomposition of the retained austenite is shifted to significantly higher temperatures. When applying appropriate austenitising and tempering parameters similar hardness and toughness properties can be achieved as for standard heat treatment condition leading to good hardness values with a fine ductile fracture surface.

Effect of Direct Ageing Treatment on Stress-Rupture Properties of GH761 Alloy

The effect of direct ageing treatment on microstructure and stress-rupture properties of GH761 alloy was studied. Phosphorus was added to the tested alloy for its beneficial effect on stress-rupture life. It was found that the grain size of the tested alloy became much finer after direct ageing treatment, in comparison with the commercial GH761 alloy under standard heat treatment condition. The optimum direct ageing treatment has been determined as follows: 830 degrees C x 4 h, air cooling+720 degrees C x 24 h, air cooling. After such treatment, the higher stress-rupture properties of the test alloy at 650 degrees C, 690 MPa were obtained. The role of phosphorus is still effective under the condition of direct ageing treatment.

The influence of thermal exposure on the γ′ precipitates characteristics and tensile behavior of superalloy IN-738LC

The effects of long term aging on γ′ size and distribution and its influence on tensile behavior of superalloy IN-738LC at room and in elevated temperatures were investigated. Samples were aged isothermally at 850 °C for different times up to 3000 h and tensile tests were performed on samples in both standard heat treatment (SHT) and aged conditions. For samples in SHT condition yield stress ( σ y) was independent of tensile temperature up to 550 °C, after which it decreased slightly and then reached a maximum at 650 °C. Also minimum ductility was observed in this temperature. For aged samples, results showed an initial decrease of σ y up to 550 °C, followed by a subsequent increase in σ y peaked at 750 °C, and decreased again at higher temperatures. Results also showed that the magnitude of the observed peak at 750 °C, increased in aged samples with increasing the aging time. Elongation for material aged for 750 h was similar to that of the material in SHT condition. For samples aged for longer times (1500 and 3000 h) no drop in ductility was observed. The observations were explained based on dislocation–precipitates and dislocation–dislocation interactions.