Procedure of Determining Creep and Creep-Rupture Strength Parameters for Isotropic Materials under Nonisothermal Loading

A procedure has been developed for determining the parameters of creep and creep-rupture strength that appear in constitutive equations of thermoviscoplasticity for describing nonisothermal processes of deformation and damage accumulation in isotropic materials due to creep. The procedure is tried out using a high-temperature chromium-nickel alloy ÉI437.     

Strengthening of threaded connections of titanium and high-temperature nickel-chromium alloys by thermovibration treatment

The article presents results of a study of the strengthening of threaded connections M6 and M8 of alloys ÉI698, VT16, and VTZ-1 by thermovibration treatment to raise their creep resistance. Treatment regimes and empirical formulas for determining the index of strengthening (for the ÉI698 alloy) are discussed. Data on long-term strength of threaded connections in initial and post-treatment states, and on the effect of aging on retention of the strengthening effect, are presented along with some mechanical and fatigue characteristics.Translated from Problemy Prochnosti, No. 9, pp. 98–103, September, 1990.     

Cyclic Crack Growth Resistance of ÉK79-ID Alloy Specimens Hardened by Surface Plastic Deformation

The influence of plastic deformation of the surface layer of ÉK79-ID alloy specimens on the characteristics of their cyclic fracture toughness is considered in the working temperature range. Plastic hardening of the surface layer is found to lead to an increase in the threshold stress intensity factor at room and elevated temperatures.     

Special Features of Creep-Crack Propagation in Refractory Nickel Alloys under Static Loading

We study creep-crack growth rate in standard specimens of alloys ÉP742 and ÉP962 at a temperature of 973 K under static loading. It is demonstrated that the alloys, which are close in chemical composition and mechanical properties, differ in creep-crack growth resistance.     

Heat resistance of nickel alloy ÉI868 with a heat protective coating

Several of the mechanisms involved in the deformation and failure of multi-layered heat resistant coatings on alloy ÉI868 during creep and thermal cycling have been studied. The effect of each of the layers in the protective coating on the development of thermal fatigue cracks, and on the heat resistance of alloy ÉI868 has been established.Strength of Materials Institute, Academy of Sciences of the Ukrainian USSR, Kiev. Translated from Problemy Prochnosti, No. 9, pp. 86–89, September, 1989.     

Influence of the Heat Treatments on Creep Behaviour of Nickel Aluminide with Boron

The nickel aluminide with boron alloy is being considered for elevated-temperature structural application in particular for jet turbine engine components. The alloy is attractive due to its ease of production, the low cost of its components, and its property advantages relative to superalloys. Therefore, if alloys based on Ni₃Al are successfully developed, substantial increases in engine performance and efficiency may be realized.The creep characteristics of an intermetallic Ni₃Al alloy containing boron produced by hot isostatic pressing were investigated in the temperature range 800 to 900^°C. Various heat treatments were used to produce different initial grain sizes of this alloy.Parameters studied were steady state strain rate, time to fracture, ductility and Larson-Miller parameter. The stress exponent, activation energy for creep and grain size exponent were calculated.It was found that by increasing the temperature of the heat treatment, the grain size increased. The results showed that the creep behaviour for this alloy improved as grain size increased. Furthermore, a comparison of the resulting creep data with data obtained from references is discussed.     

Fatigue and creep fatigue crack growth behaviour of alloy 800 at 550°C

Fatigue and creep fatigue crack growth behaviour of alloy 800 at 550°C have been studied to analyse defect assessment in a steam generator. Different grades of alloy 800 have been investigated to reproduce the in service conditions. Fatigue crack growth (FCG) tests were conducted on CT20 and tubular specimens, then on welded tubes. Furthermore the influence of hold times on fatigue crack growth behaviour was studied.

The results obtained on material simulating the weld heat affected zone are in agreement with the tests conducted on welded tubes. Fatigue crack growth characteristics of aged and cold-worked aged material seem to be slightly improved in comparison with base material. Finally a hold time of one minute increases strongly the FCG threshold value determined in pure fatigue but has a negligible influence on crack growth rates.     

GH4169合金楔横轧加工过程中动态再结晶及织构演变

为研究GH4169合金楔横轧加工过程中动态再结晶及织构演变规律,采用金相显微镜(OM)和电子背散射衍射(EBSD)对30%,50%两种断面收缩率下GH4169合金楔横轧件表层与心部的微观组织、晶体取向及织构进行分析。结果表明:GH4169合金楔横轧加工过程中,随着动态再结晶的发生,晶体取向逐渐变得随机化分布;轧制表层大角度晶界数量较轧件心部多,轧件表层织构强度变化不大,心部织构强度明显增强;经过楔横轧变形后织构发生转动,原始态织构类型为{001}〈110〉,{111}〈110〉,{111}〈011〉,轧制后主要织构类型为{001}〈010〉,{112}〈110〉,{110}〈111〉,{110}〈112〉;GH4169合金楔横轧件动态再结晶及织构演变规律是由楔横轧特殊变形特点决定的。     

Influence of Cu Addition and Microstructural Configuration on the Creep Resistance and Mechanical Properties of an Fe-Based α/α′/α″ Superalloy

Introducing Cu nanoparticles is an effective mechanism for strengthening and toughening Fe-based materials such as ultra-high-strength steels. Herein, the effect of Cu on the mechanical properties of a novel Fe-based α/α′/α″ superalloy is studied. Compared to a Cu-free reference alloy, nanoindentation reveals an increase in hardness, which was associated with the formation of Cu nanoparticles. Both alloys show room temperature (RT) compressive plastic strain at maximum stress greater than 8%, irrespective of the heat-treatment. At RT and at 750 °C, the Cu-containing alloy exhibits a slightly higher strength, but the heat treatment has a more significant impact: A configuration of α-matrix and intermetallic α′/α″-phases forming an interpenetrating network is superior to a state with isolated precipitates. This difference vanishes in monotonic creep experiments, and under the same conditions, the Cu-containing alloy exhibits a twice as high creep rate despite a slightly higher precipitate fraction. This is linked to a higher lattice misfit and faster-coarsening kinetics. Post-mortem transmission electron microscopy analysis of the creep-deformed specimens identifies dislocation bypass as the dominant deformation mechanism. However, the presence of <010>{110} dislocations in the interfacial networks and evidence of dislocation activity within α′/α″ precipitates suggest the occurrence of shearing events.     

Hot deformation behavior and processing map development of AZ110 alloy with and without addition of La-rich Mish Metal

In order to compare the workability of AZ110 alloy with and without addition of La-rich Mish Metal(MM), hot compression tests were performed on a Gleeble-3500 D thermo-mechanical simulator at the deformation temperature range of 473-623 K and strain rate range of 0.001-1 s-1. The flow stress, constitutive relation, DRX kinetic model, processing map and microstructure characterization of the alloys were investigated. The results show that the flow stress is very sensitive to deformation temperature and strain rate, and the peak stress of AZ110 LC(LC = La-rich MM) alloy is higher than that of AZ110 alloy.The hot deformation behavior of the alloys can be accurately predicted by the constitutive relations. The derived constitutive equations show that the calculated activation energy Q and stress exponent n for AZ110 alloy are higher than the calculated values of AZ110 LC alloy. The analysis of DRX kinetic models show that the development of DRX in AZ110 LC alloy is earlier than AZ110 alloy at the same deformation condition. The processing maps show that the workability of AZ110 LC alloy is significantly more excellent than AZ110 alloy and the microstructures are in good agreement with the calculated results.The AZ110 LC alloys can obtain complete DRX microstructure at high strain rate due to its higher stored energy and weak basal texture.     

High-Temperature Strength of Niobium Alloy 5VMTs with a Silicide-Ceramic Coating. Part 2. Characteristics of Short-Term Creep

The regularities of variation in the characteristics of short-term (second) creep and long-term strength of niobium alloy 5VMTs and a composite (alloy 5VMTs/silicide ceramic coating) have been studied using short test durations in the temperature range from 1770 to 2020 K. The creep strength values of the alloy and the composite have been obtained for residual strain tolerances of 0.5 and 1.0% for test durations of 0.1, 1.0, and 10 h at temperatures of 1770, 1970, and 2020 K in vacuum, an inert atmosphere, and in air.     

Creep behaviour of equiaxed fine-grain γ-TiAl-based alloy prepared by powder metallurgy

In this study, γ-TiAl-based alloy with chemical composition of Ti–45Al–5Nb (in at.-%) fabricated by powder metallurgy method was crept at 700°C under 200–500?MPa. The creep properties and the microstructure after creep tests were investigated. The results showed that the γ-TiAl-based alloy was composed of equiaxed γ-TiAl grains and α ₂-Ti₃Al grains with average sizes of 1.4 and 0.5?μm, respectively. The creep resistance deteriorated generally with increased applied stresses. The typical intergranular fracture characteristics were observed though the grains were small. The calculated stress exponent and activation energy revealed the main creep mechanism of grain boundary sliding. Furthermore, twinning and dynamic recrystallisation also led to the creep deformation.     

Impression creep behavior of Al–1.9%Ni–1.6%Mn–1%Mg alloy

In the present study, microstructure and creep behavior of an Al–1.9%Ni–1.6%Mn–1%Mg alloy were studied at temperature ranging from 493 to 513 K and under stresses between 420 and 530 MPa. The creep test was carried out by impression creep technique in which a flat ended cylindrical indenter was impressed on the specimens. The results showed that microstructure of the alloy is composed of primary α(Al) phase covered by a mantle of α(Al)+Ni₃Al intermetallic compound. Mn segregated into Al_xMn_yNi_z or Al₆Mn phases distributed inside the matrix phase. It was found that the stress exponent, n, decreases from 5.2 to 3.6 with increasing temperature. Creep activation energies between 115 kJ/mol and 151 kJ/mol were estimated for the alloy and it decreases with rising stress. According to the stress exponent and creep activation energies, the lattice and pipe diffusion- climb controlled dislocation creep were the dominant creep mechanism.     

Creep crack growth in low alloy steel weldments

Developments in the determination and analytical representation of creep crack growth property data during the past 30 years are reviewed. The testing and data analysis of weldments involve additional complexities, and these are appraised with respect to low alloy steel weldments. Creep crack initiation and growth properties are dependent on creep deformation and rupture ductility characteristics. Consideration is given to the relationship between these properties using data determined for a ½Cr½ Mo¼V/2½CrMo pipe joint.     

Special features of the variation of properties of heatshielding coatings based on zirconia in relation to loading conditions

Investigations were carried out into the effect of the conditions of thermal and force loading on the comparative characteristics of different variants of heat-shielding coatings. The results are presented on tests of thermal fatigue and thermocyclic creep of ÉI868 nickel alloy with hot-gas sprayed coatings, whose ceramic layer of ZrO₂ contained different stabilizing additions: 6.2% Y₂O₃, 8% Y₂O₃, 20% MgO, 30% CeO₂. The results show that, depending on the loading conditions, the coatings can be distributed in a sequence depending on the improvement of the properties. The highest mechanical characteristics are obtained for coatings with a ZrO₂-20% MgO ceramic layer.Translated from Problemy Prochnosti, No. 5, pp. 13–17, May, 1992.     

High-temperature characteristics of low-alloyed molybdenum alloy VM-1

The short-term static strength and momentary creep characteristics of low-alloyed molybdenum alloy VM-1 are investigated in the temperature range from 1820 to 2270 K. The creep strength values for the alloy were obtained for residual strain tolerances of 0.5 and 1.0%, the test durations of 10², 10³, and 10⁴ s at temperatures of 1820, 2120 and 2270 K. The empirical functional dependence is proposed to describe the correlation relation between the characteristics of short-term static strength, plasticity and momentary creep of the material in the thermomechanical range under study. __________ Translated from Problemy Prochnosti, No. 4, pp. 90–98, July–August, 2007.     

NiTi形状记忆合金薄膜的制备及形变特性

研究了适用于微器件的溅射态NiTi形状记忆合金薄膜.讨论了溅射工艺及织构对薄膜结构和相变特征的影响.利用薄膜热相变特性制成了微驱动器,观察并分析了该器件的形变特性.结果表明:原位加热溅射可以获得具有织构的晶化薄膜;用该薄膜制备的驱动器回复率为0.76%.     

镁合金板材的生产历史与研究现状

近年来,来自节能和环保的压力大大促进了镁合金产业的发展,具有高技术含量的镁合金板材的制备技术愈来愈受到人们关注。介绍了国内外镁合金板材的生产历史及其制备技术的研究现状,并讨论了传统制备技术和近来发展起来的几种新型轧制制备技术的特点、基本原理、研究现状及应用,对我国镁合金板材生产的发展状况进行了阐述,并提出了我国镁合金板材的发展方向。     

Heat exchange in boiling of water,ethanol, and their mixtures on a heating surface with a porous coating

Results are offered from an experimental study of boiling of water, ethanol, and their mixtures on surfaces obtained by gas-thermal deposition of aluminum oxide and alloy ÉP-616 on a vertical tube element.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 5, pp. 753–759, November, 1984.     

Rationalization and extrapolation of creep and creep fracture data for Grade 91 steel

Abstract

New relationships are shown to allow straightforward rationalization and extended extrapolation of multi-batch creep data sets for Grade 91 steel (9Cr –1MoVNb). Specifically, after normalizing the applied stress through the appropriate UTS value, creep property measurements at different temperatures are superimposed onto sigmoidal ‘master curves’ using the activation energy for lattice diffusion in the alloy steel matrix (300 kJ mol^–1). In contrast to currently-adopted analysis procedures, applying the new methodology to results from tests lasting less than 30,000 h allows the minimum creep rates, the times to various creep strains and the creep lives to be predicted accurately for stress-temperature conditions causing failure in times approaching or even exceeding 100,000 h.