Creep Resistance Of Alloy Research Articles

High Temperature Strength and Hot Working Technology for As-Cast Mg–1Zn–1Ca (ZX11) Alloy

Cast Mg–1Zn–1Ca alloy (ZX11) has been tested to evaluate its compressive strength between 25 °C and 250 °C, and workability in the range of 260–500 °C. The ultimate compressive strength of this alloy is about 30% higher than that of creep-resistant alloy Mg–3Sn–2Ca (TX32) between 25 °C and 200 °C, and exhibits a plateau between 100 °C and 175 °C, similar to TX32. This is attributed to Mg2Ca particles present at grain boundaries that reduce their sliding. The processing map, developed between 260 and 420 °C in the strain rate limits of 0.0003 s−1 to 1 s−1, exhibited two domains in the ranges: (1) 280–330 °C and 0.0003–0.01 s−1 and (2) 330–400 °C and 0.0003–0.1 s−1. In these domains, dynamic recrystallization occurs, with basal slip dominating in the first domain and prismatic slip in the second, while the recovery mechanism being climb of edge dislocations in both. The activation energy estimated using standard kinetic rate equation is 191 kJ/mol, which is higher than the value for lattice self-diffusion in magnesium indicating that a large back stress is created by the presence of Ca2Mg6Zn3 intermetallic particles in the matrix. It is recommended that the alloy be best processed at 380 °C and 0.1 s−1 at which prismatic slip is favored due to Zn addition. At higher strain rates, the alloy exhibits flow instability and adiabatic shear band formation at <340 °C while flow localization and cracking at grain boundaries occurs at temperatures >400 °C.

Present Development Status of Anti-creep Magnesium Rare-Earth Alloys

The research status of creep resistance of rare earth magnesium alloy at home and abroad is reviewed, and the mechanism of high temperature creep resistance and the way of improving the creep resistance of magnesium alloy were also discussed. The problems of high temperature resistance and creep resistance of cast magnesium alloy are pointed out, and its future development direction is forecasted. The purpose of this paper is to provide the idea and basis for the development of creep resistant and heat resistant magnesium alloy.

Pressure welding of dissimilar creep-resisting alloys and simulation of the effect of the geometrical parameters of the specimen on the localisation of plastic deformation in the pressure welding zone

Computer modelling is used to investigate the possibilities of increasing the quality of welded joints in pressure welding of dissimilar creep-resisting materials in the presence of a relief on one of the welded surfaces. It is shown that the quality of welded joints depends on the geometrical parameters of the welded specimen.

Diffusion welding of components made of creep-resisting alloys: diffusion welding of titanium-based creep-resisting alloys (Part 2)

The efficiency of using diffusion welding for joining components of nickel creep-resisting alloys is confirmed. It is proposed that the mechanical properties can be improved, the extent of plastic deformation of components reduced, and softening of the welded nickel creep-resisting alloys prevented using nickel-based interlayers.

Diffusion welding of components made of creep-resisting alloys (part 1)

The efficiency of diffusion welding components made of nickel creep-resisting alloys is confirmed. It is proposed that to increase the mechanical properties and decrease the extent of plastic deformation of components and also prevent the softening of the welded nickel creep-resisting alloys welding should be carried out using nickel interlayers.

Special features of brazing VZhM4 and VZhM5 single crystal alloys

The processes of recrystallization of single crystal nickel creep-resisting alloys in brazing were investigated. The methods of preventing recrystallization of the single crystal alloys are described. The microstructure of the brazed joints in the VZhM4 and VZhM5 alloys is investigated. The effect of heat treatment on the microstructure of the brazed joints in the VZhM4 and VZhM5 alloys is described and the strength of the brazed joints determined.

Creep Behavior of a Ru-Free Nickel-Based Single Crystal Superalloy at Medium Temperatures

By means of creep curves measurement and diffraction contrast analysis of dislocation configurations, the creep behavior and effect factors of a Ru-free nickel-based single crystal superalloy within the temperature range of 740~780°C are investigated. Results indicated that, the cubical γ′ phase transformed into the bunch-like structure. During creep at 760°C/750Mpa, no rafted features of γ′ phase is detected, but the degree of distortion of the cubic γ′ phase near fracture regions is increased. During creep, more super-dislocations shearing into γ′ phase of Ru-free alloy are decomposed on {111} plane to form the partials plus stacking fault, which is attributed to the interaction of the elements to decrease the stacking fault energy of the alloy. Moreover, the screw dislocations shearing into γ' phase of Ru-free alloy during creep at 760 °C may cross-slip from {111} to {100} planes for decomposing to form the configuration of the K-W locks, which is attributed to the higher alloying extent for decreasing the diffusion rate of elements. And the dislocation configuration may restrain the slipping of them to improve the creep resistance of alloy due to the non-plane core structure of them.

Effect of titanium additions upon microstructure and properties of precipitation-strengthened Fe-Ni-Al-Cr ferritic alloys

Various amounts of Ti (0, 2, 4 and 6 wt%) is added to a ferritic alloy with a nominal composition of Fe–10Cr–10Ni–6.5Al–3.4Mo–0.25Zr–0.005B (wt%) (FBB8). The microstructure and composition of the matrix and precipitate phases are characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). For the Ti-modified steels, the bcc ferritic matrix is strengthened by submicron L21-Ni2TiAl-type precipitates which contain (i) Fe-inclusions with the precipitates' overall diameters ranging from 100 to 500 nm for both FBB8-4 wt%Ti and FBB8-6 wt%Ti, or (ii) B2-NiAl sub-precipitates with an average diameter of 50–100 nm for FBB8-2 wt%Ti. By contrast, the Ti-free FBB8 alloy contains B2-NiAl precipitates with Fe-inclusions. The four FBB8-Ti alloys were subjected to creep experiments at 700 °C in the stress range of 60–300 MPa. Threshold stresses for all studied compositions were observed, ranging from 69 to 179 MPa, with the most creep-resistant alloy being FBB8-2Ti with L21/B2 precipitates. Based on these mechanical results and detailed electron microscopy observations, the creep mechanism is rationalized to be general dislocation climb with repulsive elastic interaction between coherent precipitates and the matrix dislocations.

Creep Rupture of the Simulated HAZ of T92 Steel Compared to that of a T91 Steel.

The increased thermal efficiency of fossil power plants calls for the development of advanced creep-resistant alloy steels like T92. In this study, microstructures found in the heat-affected zone (HAZ) of a T92 steel weld were simulated to evaluate their creep-rupture-life at elevated temperatures. An infrared heating system was used to heat the samples to 860 °C (around AC1), 900 °C (slightly below AC3), and 940 °C (moderately above AC3) for one minute, before cooling to room temperature. The simulated specimens were then subjected to a conventional post-weld heat treatment (PWHT) at 750 °C for two hours, where both the 900 °C and 940 °C simulated specimens had fine grain sizes. In the as-treated condition, the 900 °C simulated specimen consisted of fine lath martensite, ferrite subgrains, and undissolved carbides, while residual carbides and fresh martensite were found in the 940 °C simulated specimen. The results of short-term creep tests indicated that the creep resistance of the 900 °C and 940 °C simulated specimens was poorer than that of the 860 °C simulated specimens and the base metal. Moreover, simulated T92 steel samples had higher creep strength than the T91 counterpart specimens.

Influence of Cryogenic Temperatures on the Microstructure and Mechanical Properties of Magnesium Alloys: A Review

Magnesium alloys have been used in the automotive industry and 3C (computer, communication, and consumer electronics) for many years. Their room temperature properties combined with their low density offer a wide range of applications, especially when processed by High Pressure Die Casting (HPDC). The use of magnesium alloys at higher temperatures is well-studied; special creep resistant alloys containing the rare earth elements silver or yttrium are needed. However, when it comes to very low temperatures, only a few studies have been performed to determine the property-microstructure relationship. The possible fields of application at low temperatures are aerospace and satellite parts and tanks for liquefied gases. This review shall not only examine mechanical properties at low temperatures, but also the permanent effects of cyclic or long-lasting cryogenic treatment on the microstructure and mechanical properties. It was found that cryogenic treatment is able to influence the precipitate concentration and grain orientation in some magnesium alloys. Reduction in the number of brittle phases is improving ductility in some cases. It is well-known that high speed tool steels, in particular, can be influenced by cryogenic treatment. Whether this is possible with magnesium alloys and what the mechanisms are shall be reviewed.

Microstructure Evolution and Creep Properties of a Single Crystal Nickel-Based Superalloy with Various Orientations

By means of creep properties measurement and microstructure observations, the effect of microstructure evolution on creep strength of the single crystal Ni-based alloy with different orientations is investigated. Results show that, during creep at 1040 oC/137 MPa, the γ′ phase in [001]-oriented alloy is transformed into mesh-like N-type rafted structure, the one in [011]-oriented alloy is transformed into the stripe-like rafted structure along [001] direction, the one in [111]-oriented alloy is transformed into the mesh-like rafted structure along (010) plane. The γ′ phase with different configurations results in the different creep resistance of alloys, the sequence of creep resistance of alloys with different orientations are determined to be σ[001] > σ[111] > σ[011]. But after pre-compressed treated along [100] direction of [011] oriented alloy, the γ′ phase in [011] oriented alloy is transformed into the stripe-like rafted structure along [100] direction, which makes the creep life of the alloy enhancing from 11 h to 174 h at 850 oC/400 MPa, and from 74 h to 165 h at 1040 oC/137 MPa. This is attributed to the pre-treatment eliminating the gable channels to form the “labyrinth” structure of γ′ phase, which may increase the resistance of dislocation motion.

High Temperature Strength and Stress Relaxation Behavior of Dilute Binary Mg Alloys

Monotonic compression and stress relaxation tests were carried out on specimens of 6 cast binary alloys with (at. pct) 2.5 Al, 0.6 Sn, 2.2 Zn, 0.9 Nd, 0.8 Gd and 1.3 Y, and of a similarly cast AZ91D alloy for reference. The solute concentration of the binary alloys was kept deliberately low to limit precipitation hardening effects during the testing, done in the solution heat treated and quenched condition. Compression testing was carried out at 298 K, 373 K and 453 K (25 °C, 100 °C and 180 °C) for all of the alloys and at 493 K and 523 K (220 °C and 250 °C) for the Nd-, Gd- and Y- containing ones. Stress relaxation was done at 453 K (180 °C) at either a predetermined strain (0.05) or stress (150 MPa). The Mg-Al and the AZ91 alloys softened considerably above 373 K (100 °C). The rest of the alloys exhibited increasing linear strain hardening in compression and reduced stress relaxation, in the order Sn, Zn, Nd, Gd and Y, an indication of a progressively stable dislocation substructure, hence of an increasingly extended athermal regime in the strength-temperature relationship. The overall strain hardening behavior matches that of commercial alloys involving the same solutes at comparable or higher concentrations, and can be accounted for through the respective tendency of the solute atoms to develop short range order. This tendency is lowest for the near-random solid solution introduced by Al, and highest for Nd, Gd and Y, in agreement with their respective phase diagrams. The implications for creep resistant alloy selection and design are discussed.

Electrochemical-controlled Characterization of the Corrosion Fatigue Behavior of Creep-resistant Magnesium Alloys DieMag422 and AE42

Magnesium alloys offer a high potential for lightweight construction, however their application range is limited due to their low corrosion resistance. In the present study the corrosion fatigue behaviors of the creep-resistant alloys DieMag422 and AE42 were characterized and compared. In this context, fatigue properties of specimens in sodium chloride solutions as well as under simultaneous galvanostatic anodic polarization were assessed in constant amplitude tests. The results were correlated with the corrosion behavior of the alloys, which was investigated in instrumented immersion tests. Corrosion- and deformation-induced changes in microstructure were observed by light and scanning electron microscopy, yielding a structure-property relationship for a comprehensive understanding of corrosion fatigue processes. The reduction of the corrosion fatigue strength with increasing corrosion impact could be quantitatively correlated with the adjusted corrosion rates. However, different corrosion morphologies between both materials were found, leading to varying influence on the corrosion fatigue behavior.

Microstructure and tensile creep resistance of Mg-5.5%Zn-(0.7%, 1.5%, 3.5%, 7.5%)Y alloys

The tensile creep resistance of Mg-5.5%Zn-(0.7%, 1.5%, 3.5%, 7.5%)Y (mass fraction, %) gravity-casting alloys was investigated systematically. The corresponding physical models were established for analyzing the microstructure evolution and creep mechanism. The results show that four second phases are found in Mg-5.5%Zn-(0.7%, 1.5%, 3.5%, 7.5%)Y alloys, including Mg3ZnY, Mg3Zn6Y, Mg3Zn3Y2 and Mg7Zn3, where the rare earth rich phase (Mg3ZnY, Mg3Zn6Y, Mg3Zn3Y2) with high melting point can more effectively improve the creep resistance properties of alloys than Mg7Zn3. With the increasing of Y content, the creep resistance of alloys is improved correspondingly. The alloys with (1.5%, 3.5%)Y addition exhibit high creep resistance at temperatures from 175 °C to 200 °C and load from 55 MPa to 70 MPa. The 7.5%Y added alloy presents excellent creep resistance even at 275 °C and 55 MPa. The second phase which shows discontinuous distribution at the grain boundary of (0.7%, 1.5%, 3.5%)Y added alloys has preferred orientation and clogs in triple junctions of grain boundary. Simultaneously, the arrangement of second phase particles along tensile direction and the formation of denuded zones are observed during the creep process. Moreover, the crack initiates in these areas and propagates along grain boundary. Compared with discontinuous second phase, the continuous skeleton-like second phase of 7.5%Y added alloy at grain boundary has a better effect on improving the creep resistance properties of alloys.

Effect of welding methods on the structure and mechanical properties of welded joints in creep-resisting titanium alloys with different initial structural conditions

Problems of welding rotor components made of creep-resisting titanium alloys are investigated. Comparative tests of the effects of fusion welding and rotational friction welding (FW) on the structure and properties of welded joints in titanium alloys are carried out. The experimental results show that welded joints produced by rotational FW have a structure identical to the structure of the parent metal, and the heat-affected zone does not form at all. The optimum conditions of FW of creep-resisting titanium alloys are determined. Irrespective of the initial type of structure, these conditions result in the mechanical properties of the welded joint at a level of 0.9 of the properties of the parent metal.

Evaluation of Secondary Hardening and Microstructure in the Real T24 Steel Weld Joint

Development of new steels with higher creep resistance must be based on detailed knowledge of strengthening and degradation processes, structural stability at high temperature exposure and their welding. This paper is concerned with the real weld joint hardness and microstructure of progressive low alloy creep resistance T24 steel. These steel is widely used in many power-plant constructions all over the Europe. Welding the T24 steels components is one of the most important technological procedures. The aim of the performed investigation is to evaluate the hardness and microstructure in the heat affected zone (HAZ) and the weld metal. Results of the secondary hardening in the real weld joints after low temperature post weld heat treatment (460°C/48h) and without post weld heat treatment at service temperature are described in this paper. Obtained results are compared to the hardness values of the weld joint post weld heat treated at recommended temperature (740°C). The microstructure of the real weld joints was analysed by transmission electron microscopy (TEM) in order to identify minority phases - MX nanoparticles and/or coarse (M23C6) particles. Secondary hardening of the not heat treated and low temperature heat treated T24 weld joint was proved.

Influence of Discontinuous Precipitation on the Creep Behavior of a β-Solidified γ-TiAl Based Alloy

Abstract Owing to their excellent high temperature properties, intermetallic γ-TiAl based alloys are potentially suitable materials for applications in the aviation and automotive industry. In order to adjust a fine lamellar microstructure with optimum properties, the forging process is followed by a multi-stage heat treatment. During the final annealing process, a discontinuous precipitation reaction, a so-called cellular reaction, may occur which decomposes the fine lamellae in the α2/γ colonies. A stable microstructure is a crucial factor in the development of highly creep resistant alloys. In the scope of this work, various heat treatments were performed in order to adjust microstructures with a varying proportion of discontinuous precipitation. Furthermore, creep tests were performed at 800 °C and 150 MPa. Scanning electron microscopy in the back-scattered electron mode was used to characterize the microstructure's morphology. The respective phase fractions were determined by X-ray diffractometry. It could be shown that the creep resistance decreases with an increasing amount of discontinuous precipitation.

Explosion welding of high-strength bimetallic materials with a cladding layer based on niobium and nickel–cobalt alloys

The special features of explosion welding of a high-strength steel with erosion- and creep-resisting alloys are investigated. Special attention is given to the problems of producing high-quality joints in niobium and nickel–cobalt alloys with steels. A method of explosion cladding of flat and cylindrical components with these alloys is developed. The effect of the parameters of the heated gas, situated in the gap between the welded plates, on the quality of the welded joint is investigated. The results of experimental studies of the specimens of the bimetal are also presented and can be used for indicating the promising nature of further investigations in this area.

Corrosion Behavior of MRI153M Magnesium Alloy in 3% NaCl Solution

Corrosion behavior of high-pressure die cast creep resistant magnesium alloy MRI 153M in 3% NaCl aqueous solution was studied by several electrochemical and non-electrochemical techniques. The electrochemical techniques were Electrochemical Impedance Spectroscopy (EIS), Linear Polarization Resistance (LPR) and Tafel-slope Polarization. The non-electrochemical techniques were mass-loss and gas evolution measurements. Values of corrosion rates were calculated and the morphology of corroded surface studied. While corrosion rates calculated by both non-electrochemical methods are not consistent, those gained by the three electrochemical methods demonstrate consistency. In general, the rate of corrosion calculated by the gas evolution method is in a good agreement with the corrosion rate calculated from the electrochemical methods, which should be an indication of mixed chemical-electrochemical character of the process. SEM and light microscope observation of corroded specimens demonstrated the localized character of corrosion, at least at the initial stages.

Rate controlling mechanisms during hot deformation of Mg–3Gd–1Zn magnesium alloy: Dislocation glide and climb, dynamic recrystallization, and mechanical twinning

The flow behavior of the Mg–3Gd–1Zn (GZ31) magnesium alloy during hot working was critically analyzed and dislocation glide in the form of a viscous drag process (viscous glide) was identified as the rate controlling mechanism due to interaction of rare earth Gd atoms with the moving dislocations. Mechanical twinning was shown to significantly affect the level of flow stress at high Zener–Hollomon parameters, i.e. low forming temperatures and high strain rates. Moreover, dynamic recrystallization (DRX) was found to be another responsible phenomenon for deviation of constitutive equations from the theoretical ones, namely the deformation activation energy based on diffusivity and the pre-defined Garofalo’s type hyperbolic sine power, during high-temperature thermomechanical processing of this creep resistant light alloy.