High Temperature Mechanical Testing Research Articles

A Code of Practice for conducting notched bar creep tests and for interpreting the data

Fatigue & Fracture of Engineering Materials & StructuresVolume 27, Issue 4 p. 319-342 A Code of Practice for conducting notched bar creep tests and for interpreting the data G. A. WEBSTER, G. A. WEBSTER High Temperature Mechanical Testing Committee, ESIS TC11Search for more papers by this authorS. R. HOLDSWORTH, S. R. HOLDSWORTH High Temperature Mechanical Testing Committee, ESIS TC11Search for more papers by this authorM. S. LOVEDAY, M. S. LOVEDAY High Temperature Mechanical Testing Committee, ESIS TC11Search for more papers by this authorK. NIKBIN, K. NIKBIN High Temperature Mechanical Testing Committee, ESIS TC11Search for more papers by this authorI. J. PERRIN, I. J. PERRIN High Temperature Mechanical Testing Committee, ESIS TC11Search for more papers by this authorH. PURPER, H. PURPER High Temperature Mechanical Testing Committee, ESIS TC11Search for more papers by this authorR. P. SKELTON, R. P. SKELTON High Temperature Mechanical Testing Committee, ESIS TC11Search for more papers by this authorM. W. SPINDLER, M. W. SPINDLER High Temperature Mechanical Testing Committee, ESIS TC11Search for more papers by this author G. A. WEBSTER, G. A. WEBSTER High Temperature Mechanical Testing Committee, ESIS TC11Search for more papers by this authorS. R. HOLDSWORTH, S. R. HOLDSWORTH High Temperature Mechanical Testing Committee, ESIS TC11Search for more papers by this authorM. S. LOVEDAY, M. S. LOVEDAY High Temperature Mechanical Testing Committee, ESIS TC11Search for more papers by this authorK. NIKBIN, K. NIKBIN High Temperature Mechanical Testing Committee, ESIS TC11Search for more papers by this authorI. J. PERRIN, I. J. PERRIN High Temperature Mechanical Testing Committee, ESIS TC11Search for more papers by this authorH. PURPER, H. PURPER High Temperature Mechanical Testing Committee, ESIS TC11Search for more papers by this authorR. P. SKELTON, R. P. SKELTON High Temperature Mechanical Testing Committee, ESIS TC11Search for more papers by this authorM. W. SPINDLER, M. W. SPINDLER High Temperature Mechanical Testing Committee, ESIS TC11Search for more papers by this author First published: 11 March 2004 https://doi.org/10.1111/j.1460-2695.2004.00765.xCitations: 78 Correspondence: G. A. Webster. E-mail: g.webster@imperial.ac.uk Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume27, Issue4April 2004Pages 319-342 RelatedInformation

A Code of Practice for the determination of cyclic stress-strain data

There are no procedural standards for the determination of stress-strain properties where a reversal of stress is involved. The purpose of this Code of Practice is to detail the requirements for cyclic stress-strain (CSS) testing on uniaxial testpieces. CSS testing may entail the use of a single testpiece to produce data over several strain ranges. Alternatively, data from a number of constant strain range tests may be obtained, for example as the by-product of a series of low cycle fatigue (LCF) endurance tests. Procedures for LCF testing are covered by a number of existing Codes of Practice and Standards [1–6], and this document does not recommend any alteration to these. This Code of Practice has been prepared by the CSS Working Party of the ESIS TC11 High Temperature Mechanical Testing Committee.Historically, CSS results have been reported in terms of a relatively simple power law. However, engineers involved in design and assessment activities are now increasingly tending to use more advanced constitutive relations such as the Chaboche equations [7]. Hence, the model equations available to characterise CSS behaviour cover a range of complexities, with the approach selected being determined by the requirements of the end-user application. These will be influenced by such factors as the type and history of loading, the operating temperature and presence of thermal gradients, the variation of cyclic plastic strain within the component, and the need to determine absolute magnitudes or ranges of stress and strain. The laboratory test procedures defined in this Code of Practice are capable of generating the CSS data required for the full spectrum of model equations currently used in engineering assessment.In addition to recommending best laboratory practice, this document includes sections on engineering requirements, test data analysis (including the connection between alternative forms of model equation), and the exploitation of existing data. Advice is also given for those circumstances where testpiece material is limited, thus requiring quick methods of data acquisition using block loading techniques. In all cases, the use of cylindrical testpiece gauge lengths is recommended, and only isothermal testing at appropriate temperatures under strain-controlled conditions is covered.

Synthesis of a Metallic Ceramic -Ti3SiC2 by PDS Process and its Properties

ABSTRACTPowder mixtures of Ti/Si/C, Ti/SiC/C, Ti/Si/TiC, Ti/SiC/TiC and Ti/TiSi2/TiC were used for the synthesis of Ti3SiC2 by using a pulse discharge sintering (PDS) process. The Ti/Si/TiC powder was found to be the best among the five powder mixtures for the Ti3SiC2 synthesis. The highest content of Ti3SiC2 can be improved to about 99wt% at the sintering temperature of 1300°C for 15 minutes. The relative density of all the synthesized samples is higher than 98–99% at the sintering temperature above 1275°C. The nearly single phase Ti3SiC2 was found to show plastic deformation at room temperature and a good machinability. Both electrical and thermal conductivity were found to be more than two times of the value of a control pure Ti sample. The high-temperature mechanical tests confirmed that the Ti3SiC2 samples synthesized by the PDS process displayed a comparable performance with those fabricated by the other techniques.

Current understanding of superplastic deformation of Y-TZP and its application to joining

A review of the high-temperature, steady-state creep of yttria tetragonal zirconia polycrystals (Y-TZP) as a function of grain size, strain rate, stress, and temperature will be presented in this paper. Data have been analyzed using the standard creep equation incorporating a threshold stress. Microstructural observations of deformed samples indicated that deformation was achieved primarily by grain boundary sliding (GBS). This microscopic characteristic was used to join pieces of these materials. When two pieces of ceramics are compressed in the superplastic regime, GBS will produce a junction between the pieces. Several types of strong junctions have been produced, i.e. between pieces of the same material having different grain sizes, and between pieces of different materials. Scanning electron microscopy of the interfaces showed that each interface was cavity- and crack-free. Vickers indentations and high-temperature mechanical tests indicated that the interfaces were as strong as the matrix. This joining technique allows the construction of a complex shape or a functional gradient material.

Brittleness of steels at near-solidus temperatures (current state of the problem)

1. High-temperature brittleness of steels is observed in the temperature range 0.90–0.99T melt and is characterized by a narrow temperature range (generally not exceeding 10°C) in which the ductile and strength parameters are not affected by the deformation rate. In this range the steels fracture by a grain-boundary mechanism with the formation of a characteristic molten relief. 2. The temperature of the ductile-brittle, transformationT d/b (the temperature of zero ductility) is most affected by C. S, P, and B; an increase in their content diminishesT d/b. The addition of manganese and the treatment of the melt with REM and AEM weaken the effect of sulfur and increase the temperatureT d/b by 10–100°C. 3. Most investigators attribute the appearance of the ductile-brittle transformation at near-solidus temperatures to the early melting of grain boundaries. The problems of the mechanism of formation and the chemical composition and role of the liquid phase in the evolution of grain-boundary fracture requires additional theoretical and experimental studies. 4. The available data (the “abrupt” behavior of the curves of ductile-brittle transformation, the experimentally determined liquid layers atT=T d/b) show that the temperature of grain-boundary melting can be determined using the method of high-temperature mechanical tests and can be understood as the temperature of the ductile-brittle transformationT d/b. 5. The temperature of grain-boundary melting in tool steels R6M5 and R18 coincides with the temperature ranges of heating for quenching recommended by GOST 19265-73, which should be taken into account in practical heat treatment because the melting of grain boundaries can be a cause of instability of the mechanical properties of small-size tools.

Physical mechanisms of helium release during deformation of vanadium alloys doped with helium atoms

Helium embrittlement of vanadium alloys which are labored for future fusion reactors may be closely related to the transport of helium to critical failure sites within the material (grain boundaries, precipitates, etc.). Recently during high-temperature mechanical tests of helium-doped vanadium alloys by the tritium trick technique, the abnormal helium release peaks have been observed. In this case, a good correlation has been found between the helium release during the deformation and embrittlement processes. Such results have fundamental meaning for understanding the helium behavior during deformation of fusion structural materials. In the present paper, the physical mechanisms of abnormal helium release from deforming vanadium alloys are suggested. The theory of helium release is based on the dynamic-diffusion models of dislocation motion with helium atoms and helium bubbles, where helium atoms and helium bubbles are swept by moving dislocations. In the suggested model, the effect of the strain rate of plastic deformation and pipe diffusion of helium atoms along dislocations on this phenomenon is considered. The theoretical models are compared with experimental results for helium release during deformation of vanadium alloys after helium doping by the tritium trick technique. The temperature dependence of this phenomenon and the effect of strain rate on growth kinetics of helium bubbles are analyzed. The present results allow us to understand the effect of various helium doping techniques (helium trick, cyclotron preimplantation and boron-10 technique) on helium release from deformed vanadium alloys.

Hot friction testing of ceramics

Reciprocating tests were carried out on a number of different ceramics at a range of temperatures up to 1450 °C in a high precision test system. The friction that was generated, and the damage to surfaces, were investigated. The aim of the experiments was to investigate the tribology of high-temperature ceramic contacts, and to provide data for high-temperature engineering applications of ceramics. In particular, information was needed on the friction and surface damage that occurs at the contacts between the test jig parts (made from ceramic) and ceramic test samples used for high-temperature mechanical testing. Significant errors in test results are likely to occur because of frictional effects, and it is important to measure and make allowance for this effect. The tests were carried out with both a sliding contact geometry, and also with a rolling contact. A range of ceramics were examined, including alumina, silicon nitride, silicon carbide, partially stabilised zirconia and soda-lime glass under a range of different loads and temperatures. The friction and surface damage generated in rolling contact were lower than those in sliding contact, with friction coefficients in the range 0.02–0.05 compared with sliding contact values rising from 0.2 in most cases at room temperature to 0.4–1 at higher temperatures. For the silicon-based non-oxide ceramics, oxidation of the test surfaces was found to occur, leading to the formation of glass at the wear interface at high temperature. In some tests where glass was formed, or was one of the bulk samples, pronounced stick-slip was observed above a critical temperature. The key recommendation for the study for high-temperature mechanical testing of ceramics is that rolling contact elements produce negligible errors in the results of strength tests, and so should be used wherever possible.

High-temperature dynamic mechanical testing of ceramic fibers: Apparatus and preliminary results

A test apparatus is described for the dynamic testing of single ceramic fibers from room temperature to 1600°C using forced vibration sine wave displacements from 0.1 to 25 Hz. Both storage (elastic, real or in-phase) and loss (dissipative, imaginary or out-of-phase) components of the dynamic modulus are obtained. The deconvolution equations required to extract isothermal data from a non-uniform (parabolic) temperature distribution are presented. Preliminary data on sapphire filaments and CVD silicon carbide fibers are discussed. The results show the validity of the testing method and data, which are in good agreement with available literature data on similar materials.

Melt-Processed Ni3Al matrix composites reinforced with TiC particles

TiC-reinforced Ni3Al metal matrix composites have been investigated. The composites were prepared by in situ precipitation of either 0.01, 0.05, or 0.1 vol fraction TiC in molten Ni3Al. These precipitates are thermodynamically stable in the Ni3Al at 1000 °C up to 50 hours. Although almost ideal precipitate distribution was achieved at low volume fraction of TiC, at higher volume fraction, there was a tendency toward agglomeration. Room and hightemperature mechanical testing showed significant improvement in modulus, yield strength, and ultimate tensile strength, while still maintaining a 2.5 pct elongation at 0.1 vol. fraction TiC and 500 °C. The density of precipitates (number/m3) is strongly dependent on the fraction of TiC, on temperature, and on the holding time at that temperature. The critical nucleation temperature for these precipitates was determined to be at 1475 °C. Experimentally evaluated growth rate constants indicate a diffusion-controlled coarsening mechanism along with coalescence and multiparticle interaction at higher volume fractions of TiC. This is in accordance with either the Lifshitz Slyozov Encounter Modified (LSEM) model or with the Voorhees and Glicksman (VG) model.

Microstructural characterization of precipitates formed during high temperature testing and processing of iron-aluminide alloys

Iron-aluminide alloys were examined using analytical electron microscopy after creep-rupture testing at 600–650°C or after thermomechanical processing at 650–1250°C. Various precipitates were found in several different alloys after testing or heat treatments and most were identified as carbide phases. Small Mo 2C grain boundary precipitates and occasional coarse FeAlMo Laves phase particles were found after creep testing at 650°C in ternary Fe 3Al+2Mo alloy, but only after 0.3 h at 275 MPa and not after 90 h at 69 MPa. Large and small niobium- and zirconium-rich MC unintentional impurities) creep tested for 1932 h at 650°C and 69 MPa, whereas no such precipitates were observed when creep-rupture occured after only 0.5 h at 275 MPa. Two different precipitate phases were found in a complex Fe 3Al+Cr, Mo,Ti,Nb,V,C alloy after high temperature processing or mechanical testing, a titanium-rich MC phase and a CrMoFe phase (Fe 2MoC?). Coarse matrix particles of both phases were found after hot rolling at 650°C. The precipitates partially dissolved and only MC remained after solution annealing (SA) at 1100–1200°C, but finer grain boundary MC was found after a SA treatment at 1250°C. The CrMoFe phase was not found after the SA treatments, but was found to form around matrix MC particles during creep at 600°C (207 MPa for 244 h) and during aging for 9 h at 750°C.

α-β型チタン合金の組織制御を施した素粉末混合法による高性能化

A variety of α-β titanium alloys were produced by the microstructure-controllable new Blended Elemental (BE) P/M method, in which as-sintered material is water-quenched from the β-phase region prior to HIP 'ing, with emphasis on relating composition/processing/microstructure to mechanical properties. Alloy composition was found to have a strong effect on the microstructure. In near α type α-β alloys such as Ti-6Al-2Sn-4Zr-2Mo, the new BE method created a fine two phase structure in a relatively small β grain with lower aspect ratio α-platelets. This microstructure resulted in improved high cycle fatigue strength compared to those for conventional BE alloy. In contrast, in β-rich α-β alloys such as Ti-5Al-2Cr-1Fe, a massive α phase was formed on prior β grain boundaries. In this case poor improvement in fatigue strength was obtained because of the presence of this massive α. High temperature mechanical tests done on near α type alloys revealed that both creep resistance and low cycle fatigue strength were superior in new BE material than in conventional BE material. These findings demonstrated that the new BE method applied to near α type α-β alloys can give rise to better balance of mechanical properties compared with that of ingot metallurgy.

A CODE OF PRACTICE FOR CONSTANT‐AMPLITUDE LOW CYCLE FATIGUE TESTING AT ELEVATED TEMPERATURES

Abstract— This paper comprises the text of a code of testing practice prepared under the auspices of a British High Temperature Mechanical Testing Committee. The code makes recommendations concerning equipment, test specimens and procedures; it includes several explanatory and cautionary notes and references to related standards and publications. It was considered that the American National Standard ASTM E606–80 [1] contained much of the required material and in order to avoid unnecessary divergence of practice the recommendations therein have been used as far as possible but with specific modifications and additions to account for current UK needs and practice. It is anticipated that this document may form the basis of a future BSI publication and consequently, the general format is similar to that recommended by BSI in BS O 1981 [2]. Currently a programme of intercomparative Low Cycle Fatigue testing is being carried out under the auspices of and with support from the Community Bureau of Reference (BCR) of the Commission of European Communities. This programme will shortly be widened to include non‐European countries as part of a broader initiative in the field of Materials and Standards (VAMAS). In consequence it is intended to consider and, if necessary, revise the Code of Practice in the light of results from this programme and of other on‐going work in the field.

SINTERING AND CHARACTERIZATION STUDIES OF NiO

High purity NiO polycrystals have been prepared by hotpressing and by sintering. They were characterized by optical and electron microscopy. Their creep behaviour was studied above 1200°C. I INTRODUCTION Nickel oxide polycrystals have been prepared with the aim of studying their plastic deformation. For mechanical testing, materials with stabilized microstructure (grain size, porosity, ...) are needed. We have prepared NiO polycrystals two ways similar to those previously used for NiO/l/ or Co0/2,3,4/ and characterized the resulting specimens by microstructural observations and creep testing. I1 PREPARATION OF POLYCRYSTALS 11-1 Initial sintering The starting powder was high purity NiO provided by Johnson-Matthey (total impurity content below 15 ppm) with an average particle size of 0.1 Qm. The powder was first cold-pressed in a die under 400 MPa. It was then annealed 3 days in air at 1200°C on a boat made of NiO to avoid contamination. The density of the sintered body was 65 % of the theoretical density taken as 6.8 g/cm3 and the grain size of the order of 1 vm. Such a material is not appropriate for high temperature mechanical testing and two types of additional treatment were required. 11-2 Ultra-high temperature sintering Since most of the creep tests were to be performed below 1400°C, sintering treatments between 1500°C and 1700°C (0.80 TM and 0.88 TM ; TM = 2230 K, melting temperature) were performed in air during 3 days. To avoid contamination, the specimens were separated from the alumina crucible by a bed of NiO. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986157

Influence of the critical stage of polygonization on the characteristics of ductility of tungsten in high-temperature mechanical tests

Influence of the critical stage of polygonization on the characteristics of ductility of tungsten in high-temperature mechanical tests

Unit for high-temperature mechanical tests in a complex stress state

Unit for high-temperature mechanical tests in a complex stress state

A Short-Time, High Temperature Mechanical Testing Facility

Abstract Design and performance details are given for a facility developed to obtain the mechanical properties of materials under high heating rate or transient temperature conditions and medium strain rates. The system uses self-resistance heating and is applicable to materials possessing electrical resistivities ranging from that of aluminum to that of graphite. Heating rates as high as 2000 K/s in graphite are attained under controlled conditions. Methods of measuring temperature and the effects of expected temperature distributions are discussed. A method for measuring strain during transient temperature conditions to 3000 K is described. Finally, results are presented for the stress-strain behavior of Type 316 stainless steel and ATJ(S) graphite obtained for heating times of few seconds.

Choice of a getter for the high-temperature mechanical testing of niobium and its alloys

The high-temperature creep properties of Nb were studied. It was found that in determining the high-temperature creep characteristics of niobium in testing machines with oil-vapor vacuum pumps, porous titanium getter provides effective protection, if at the same time the working part of the specimen is screened with niobium foil. (JRD)

Structural changes in certain modified 12% chromium steels

1. The structure of 12% Cr steels containing substantial amounts of tungsten (3–4%) and also molybdenum and vanadium, which results in a heterogeneous structure, is unstable at the service temperatures, since the δ-ferrite decomposes and gives rise to precipitation hardening. 2. Electron microscopy and X-ray analysis of electrolytically extracted residues showed that the phase Fe2W precipitates from the δ-ferrite during extended heating. 3. High-temperature mechanical tests showed that decomposition of the δ-ferrite did not reduce the creep strength. 4. The analyses made indicated that the effect of small additions of vanadium and molybdenum in the presence of tungsten is advantageous, although the validity of this conclusion may be very limited. 5. Our tests confirmed that a very high δ-ferrite content reduces the impact toughness.

オーステナイト・ステンレス鋼の高温特性について

In order to present some information for design criteria about high-temperature properties of austenitic stainless steels, some results of high-temperature mechanical test which had been previously reported through our research were summurized and discussed.Six standard type austenitic stainless steel rolled bars of AISI 304, 316, 321, 347 and 318 were used for high-temperature mechanical testing, such as, short-time tensile, creep-rupture, fatigue tests and testing for embrittlement associated with the structual change in these alloys.Of course, it depends on the service condition of the materials which property should be taken for the allowable stress. In the case of stainless steels, however, the allowable stress in lower temperature range can be usually obtained from yield strength, and higher temperature range, from limiting-creep stress. As it has been shown that the temperature dependance of fatigue strength of these alloys is not so remarkable as that of limiting-creep stress, fatigue strength should be first considered as allowable stress in lower temperature range. As the caracteristics of austenitic stainless steels, it was recognized that the ratio of the tensile, fatigue and rupture strength to the yield strength or limiting-creep stress was relatively high.Consideration for embrittlement at grain boundary which may be predominant in some austenitic alloys must be taken, while setting up the criterion on load-carring-ability as described in the above. Type 316, 318 and 310 stainless steels are liable to show intergranular brittlement due to massive precipitates of chromium carbide, sigme phase or other intermetallic compounds at grain boundaries. Grain boundary precipitation affects the alloys, making them more brittle and promoting the fructure at grain boundary in rupture testing.

Apparatus for long period temperature - stress tests on metals

The paper describes an apparatus for high temperature mechanical testing suitable for accurate determination of creep and allied effects. The apparatus includes a sensitive extensometer and a method for very close control of the temperature of the specimen heated in an electric resistance furnace. The method makes use of a platinum resistance coil placed in the furnace, and which forms part of a Wheatstone Bridge and through a control indicator and relay operates the adjustment of the furnace current to compensate for minor fluctuations from various causes. The form of testing machine and layout are described, and the order of sensitivity indicated.