Effect of Hot Isostatic Pressing on Microstructures and Stress-Rupture Properties of CM 939 Weldable Alloy

Effect of hot isostatic pressing (HIP) treatment on the microstructure and the stress rupture properties of CM 939 Weldable alloy have been investigated. The results shown that the HIP has the function of densification and homogenization, all of the microporosity have been almost removed, the segregation of the alloy have been reduced, the microstructure became better, the stress rupture life of CM 939 Weldable alloy have been obviously improved, Meanwhile, the data dispersion of stress rupture properties have been reduced for the alloy after HIP.

Strain response of fiber-reinforced ceramic-matrix composites subjected to stress-rupture with stochastic load at intermediate temperature

To ensure the reliability and safety of ceramic-matrix composites (CMCs) hot-section components used in the aero engines, it is necessary to perform the strain response of CMCs at intermediate temperatures (600 to 1000 °C) under stress-rupture with stochastic loading. In this paper, the strain response of SiC/SiC composite under stress-rupture with stochastic load at intermediate temperatures is investigated. Multiple damage mechanisms of matrix cracking, interface debonding and oxidation, and fiber’s oxidation and fracture are considered. Matrix crack spacing, interface oxidation and debonding length, fiber’s broken probability, and intact fiber’s stress are determined using micromechanical damage models. Experimental strain response and internal damage evolution of SiC/SiC composite under constant and stochastic stress are predicted. Effects of stochastic stress level and stochastic time, material properties, damage state and environment temperature on composite’s strain response and stress-rupture life are discussed. When stochastic stress level and environment temperature increase, the composite’s strain at the stochastic stress increases, the time for the interface complete debonding and oxidation decreases, and the stress-rupture life decreases.

Stress Rupture Behavior of Disk Superalloys Exposed to Low-Temperature Hot Corrosion Environment

Siemens Energy has a large fleet of aero-derivative gas turbines. The performance and durability of these power turbines largely depend on the capability of hot section components to resist high-temperature surface attacks and to maintain their mechanical properties. Hot corrosion attack occurs due to exposure of turbine components to sulfur-bearing fuels/air together with other corrosive compounds during turbine operation. This paper investigates the impact of low-temperature hot corrosion on the stress rupture of commonly used gas turbine disk alloys, including Inconel 718, Incoloy 901, and A-286. The results indicate that Inconel 718 and Incoloy 901 maintain their creep strength advantage over A-286 in a low-temperature hot corrosion inducing environment at 1100°F. All three materials exhibited an equivalent life reduction in the corrosive environments at 1100°F. Moreover, the results demonstrate that the stress-rupture life of materials in hot-corrosion environments depends on the combined and cumulative effects of corrosion-resistant and hardening elements.

Evaluation of Platform Weld Repairs on F-Class, Stage 1 Buckets

The higher turbine inlet temperatures coupled with dry low emission combustors on the widely used F-class gas turbines produces high heat loadings on the stage 1, hot section components, particularly focused on the platform section of rotating buckets/blades. This paper provides a brief design and durability history overview of the platform areas of buckets. High heat loadings combined with cyclic operation, and variation in casting supplier quality, resulted in various levels of extensive cracking and high scrap rates based on prior conservative repair limits. Currently, the consensus amongst repair shops is that platform cracking extending beyond a limited area near the edge is irreparable, and the bucket/blade should be scrapped. As repair technology is ever changing and evolving, what once was a limit may now be excessively conservative. To reduce scrap frequency and increase component repair yields, newer weld filler materials and alternative welding processes were tested and evaluated. Metallurgical evaluation of various types of weld filler metals as applied to the platforms of F-Class, first stage buckets cast from DS GTD111 material were undertaken. The buckets were equally processed up to but excluding weld filler and weld process type. The bucket platform welds were then simultaneously evaluated via optical microscopy. Crack free weld repairs, conducted on engine run platforms, given the appropriate heat treatments, pre- and post-welding, can be achieved with solid solutioned strengthened Inconel 625 filler, and low volume fraction gamma prime strengthened Nimonic 263 filler using conventional GTAW. Crack free weldments or minor cracking (cracks of a small number and length) can also be achieved using Laser Cladding and/or elevated temperature GTAW with IN-738 filler metal. Surprisingly the newer weld filler metal Haynes 282 and older/traditional Haynes 230, showed evidence of hot-cracking and/or micro-fissuring (strain age cracking. A large number and length of cracks was observed when using Waspaloy as the weld filler metal. Tensile and stress rupture testing of various types of welds as applied to the platform areas were also undertaken to down-select the best filler metal. Samples were removed from the platform area of engine run buckets. Some samples were then used to obtain a baseline set of parameters of the base material. Other samples were used to test weldments of various filler metals and weld processes against those baseline values obtained. Testing of elevated temperature GTAW weldments and laser cladding with IN-738 filler metal as well as conventional GTAW with Haynes 282 filler metal produced satisfactory tensile strength and ductility properties. Elevated temperature welds using IN-738 filler were able to achieve between 76–79% stress rupture life of the base metal, while laser cladding using the same filler only yielded a 60–64% value of the base material stress rupture life. The GTAW Haynes 282 samples yielded approximately between 57–64% of the base material stress rupture life. Based on the test results, the recommended procedure for GTD111DS blade platform weld repair is to use IN-738 weld filler with the elevated temperature GTAW process.

Influence of Phosphorus Addition on the Stress Rupture Properties of Direct Aged IN706 Superalloy

This study investigated the influence of phosphorus (P) addition on the stress rupture properties of direct aged IN706 superalloy. The results showed that P slightly improved the stress rupture life of the superalloy when added in the range between 0.002% and 0.008%; however, it significantly reduced the stress rupture life when added in the range between 0.013% and 0.017%. Microstructure characterization indicated that the precipitation of γ′, γ″, and η phases was not significantly affected by the addition of P. Phosphides precipitated in the alloy containing 0.017% P after aging at 980 °C for 10 min. Compared to a similar study previously made on IN706 superalloy, it was found that the optimum P concentration in the as-solutioned state for improving the stress rupture properties was not definite. Furthermore, the relationship between the amount of P segregated at the grain boundary and the role of P on the stress rupture properties was discussed.

Influence Mechanism of Silicon on Carbide Phase Precipitation of a Corrosion Resistance Nickel Based Superalloy

The effect of silicon on diffusion behavior of the carbide forming elements in Ni-Mo-Cr-Fe based corrosion-resistant alloy is studied by diffusion couple experiment. One group of diffusion couples are made of the alloy with a different silicon content, another group of diffusion couples are made of pure nickel and the alloy with different silicon content (0Si, 2Si). Two groups of alloys with same silicon content and different carbon content are also prepared, the microstructure of solution and aging state of these two groups alloys are analyzed, and their stress rupture properties are tested. The effect of silicon on the diffusion of alloy elements and the interaction effect of carbon and silicon on the microstructure and stress rupture properties of the alloy are analyzed. The mechanism of Si on the precipitation behavior of carbide phase in Ni-Mo-Cr-Fe corrosion resistant alloy is discussed. The results show that silicon can promote the diffusion of carbide forming elements and the formation of carbide. The precipitation behavior of the secondary phase is the result of the interaction effect of silicon and carbon, and is related to the thermal history of the alloy. Combined with the characteristic of primary carbides, it is confirmed that the precipitation of M12C type secondary carbide is caused by the relative lack of carbon element and the relative enrichment of carbide forming elements such as molybdenum. The stress rupture properties of two silicon-containing alloys with different carbon contents in solution and aging state are tested. The stress rupture life of low carbon alloy is lower compared with high carbon alloy at solution state, but after aging treatment, the stress rupture life of low carbon alloy is significantly improved, and higher than that of high carbon alloy. The main aim of this research is to reveal the influence mechanism of silicon on carbide phase precipitation of a Ni-Mo-Cr-Fe based corrosion-resistant superalloy, which provides theoretical basis and reference for later alloy design and engineering application.

Heat Treatments Effects on Nickel-Based Superalloy Inconel 713C

The purpose of this work is to study the effect of heat treatments on the microstructure of the nickel-based superalloy Inconel 713C. Three different conditions were studied and the results compared: (1) as cast; (2) solid solution treatment (1179 °C/2 h) and (3) stabilization heat treatment (1179 °C/2 h plus 926 °C/16 h). Inconel 713C is normally used in the as-cast condition, an improvement in the 980 °C stress-rupture life is often obtained by a solution heat treatment. However, the material in this condition tested under high stress at 730 °C shows a marked decreased in rupture life and ductility. The mechanical resistance in creep increases in Inconel 713C by precipitation hardening phase, with γ’ (Ni3Al) formed during the heat treatments. The characterization techniques used were: chemical analysis, hardness testing, X-ray diffraction, optical microscopy and scanning electron microscopy (SEM), EDS analyzes and thermocalculation. The SEM and EDS analysis illustrated the γ, γ’ and carbides. The matrix phase (γ), has in its constitution the precipitation of the γ’ phase, in a cubic form, and in some regions, carbides were modified through the heat treatments. (M23C6-type) and boride (M3B2 type) identified with the use of the thermocalculation. The heat treatments increase the relative intensity of niobium in the carbides. The hardness test was not achieved because the material was overaged.

Heat Treatments Effects on NickeI-Based Superalloy Inconel 713C

The purpose of this work is to study the effect of heat treatments on the microstructure of the nickel-based superalloy Inconel 713C. Three different conditions were studied and the results compared: (1) as cast; (2) solution treatment (1,179°C/2h) and (3) stabilizing treatment (1,179°C/2h plus 926°C/16h). Inconel 713C is normally used in the as-cast condition, an improvement in the 980°C stress-rupture life is often obtained by a solution heat treatment. However, the material in this condition tested under high stress at 730°C shows a marked decreased in rupture life and ductility [1]. The mechanical resistance in creep increases in Inconel 713C by precipitation hardening phase, such γ’ (Ni3Al) formed during the heat treatments [2]. The characterization techniques used was: chemical analysis, hardness test, X-ray diffraction, optical microscope and scanning electron microscopy (SEM), EDS analyzes and thermocalculation. The heat treatments modified the dendritic structure, reducing the acicularity. The SEM and EDS analysis illustrated the γ, γ’ and carbides. The matrix phase (γ), has in its constitution the precipitation of the γ’ phase, in a cubic form, and in some regions, veins of carbides were modified with the heat treatments.