摘要:

AbstractThere is considerable interest in determining the fracture toughness of brittle materials by measuring the extent of cracking associated with a Vickers indentation because of the ease of specimen preparation and the simplicity of the test. However, confusion has been engendered by the multitude of models and equations in the literature relating the degree of cracking to the fracture toughness. In Part 1 of this work, nineteen of these equations are reviewed and then modified in a standard manner for both experimental convenience and direct comparison.MST/1050a

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.9.865

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractAn investigation including the use of transmission electron microscopy has been carried out into the solid state transformations in Ti–Al–Ru alloys in the composition range 17–37 at.-%Al and 1–5 at.-%Ru. Ruthenium is shown to be a strongβstabiliser: a 5 at.-%Ru addition produced complete or substantially complete retention of metastableβon quenching from 1250°C (within the stableβrange). Three types of martensite can result by quenching from theβfield, depending on the composition: a hexagonal martensiteα′inα+α2alloys with 1 at.-%Ru, an ordered hexagonal (DO19) in alloys close to Ti3Al stoichiometry with 1 at.-%Ru; an orthorhombic martensite inα+α2alloys with 2 at.-%Ru. On heating martensite or retainedβin the range 1100–770°C, various transformations occur depending on composition and temperature, e.g. tempering of martensite toα2+βorα2+γ+ G, or reversion of martensite toβfollowed by precipitation of one or more of the phasesα,α2andγ.MST/1029

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.9.873

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractMechanisms influencing the ambient temperature mechanical properties of commercial Al–Li alloys 2090, 8090, 8091, and 2091 are examined as a function of plate orientation, with specific emphasis on the role of microstructure. In Part 1, results on the uniaxial tensile and plane strain fracture toughness properties are presented and the behaviour is discussed in terms of the role of the matrix and grain boundary precipitates, associated precipitate free zones (PFZs), and the occurrence of short-transverse delamination. It is seen that in general peak aged microstructures show an excellent combination of strength and toughness (L–T, T–L), equal to or exceeding that shown by traditional 2000 and 7000 series high strength aluminium alloys. The superior toughness of peak aged compared with naturally aged microstructures seems to be associated with widespread matrix precipitation of platelike precipitates (T1in Al–Li–Cu alloys and S in Al–Li–Cu–Mg alloys),β′-dispersoids and second phase particles which promote ductile (void coalescence) fracture, and with secondary cracking (through thickness delamination) caused by poor short transverse properties. By contrast, the deterioration in fracture toughness with overaging is primarily attributed to extensive grain boundary precipitation and corresponding formation of PFZs, similar to traditional aluminium alloys. All alloys show highly textured, predominantly unrecrystallised grain structures that render the properties to be strongly orientation dependent; specifically, fracture toughness values for the short-transverse orientations (S–L, S–T) are typically 50% lower than in the longitudinal and transverse orientations.MST/926a

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.9.882

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractMechanisms influencing the ambient temperature mechanical properties of commercial Al–Li alloys 2090, 2091, 8090, and 8091 are examined, with specific emphasis on the role of microstructure. In Part 2, results on fatigue crack propagation behaviour are presented for both‘long’(≥5 mm) and‘microstructurally small’(~1–1000μm) cracks and compared with behaviour in traditional high strength aluminium alloys. In general, it is found that the growth rates of long fatigue cracks in Al–Li alloys are up to two to three orders of magnitude lower than in traditional 7000 and 2000 series alloys, when compared at an equivalent stress intensity range∆K. By contrast, corresponding growth rates of microstructurally small fatigue cracks were up to two to three orders of magnitude higher than the long crack results. Such observations are attributed to the prominent role of crack tip shielding in Al–Li alloys resulting from the tortuous and deflected nature of the crack paths which results in a reduced crack tip‘driving force’from crack deflection and, more importantly, from the consequent crack closure induced by the wedging of fracture surface asperities. Since microstructurally small cracks are unable to develop the same level of shielding from crack closure by virtue of their limited wake, small crack growth rates are significantly accelerated. Unlike fracture toughness behaviour, artificial aging of commercial Al–Li alloys to peak strength has a mixed influence on the (long crack) resistance. Although behaviour at higher growth rates is relatively unaffected, in 2091 nominal threshold∆KTHvalues are increased by 17%, whereas in 8090 and 8091 they are decreased by 16–17%. However, all alloys show reduced effective fatigue thresholds at peak strength after correcting for crack closure.MST/926b

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.9.896

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe characteristics of serrated yielding (the Portevin–Le Chatelier effect) in a Nb–V dual phase steel have been studied in the temperature range 85–210°C at strain rates between 1·2×10−5and 1·2×10−2s−1. Serrated yielding was found to initiate only after a critical strainɛcwas reached. The strain between two successive serrations∆ɛsincreases almost linearly with strain, while the stress drop∆σcincreases with strain up to∆σmax, then decreases. The exponentβin the mobile dislocation density–plastic strain relationship (ρm=ɛβ) is 1·09 in the temperature range 85–140°C and 1·34 in the temperature range 140–210°C. The results also indicate that in the same temperature ranges there are two values of activation energy for type A serrations, i.e. 79 and 119 kJ mol−1respectively. The results are discussed in terms of substitutional–interstitial solute atom interaction and changes of concentration of interstitial atoms.MST/934

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.9.908

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractBased on the three parameter Weibull distribution of the critical stress required for the cracked martensite–austenite (M–A) constituent to initiate cleavage, a statistical model has been derived of the transgranular cleavage fracture in granular bainite in weld heat affected zone. From the assumption that cleavage fracture is the result of the statistical competition between microcracks of various sizes in a stress field, a new definition of cleavage fracture stress is given by using the statistical model, further developed to take account of the particular stress distribution in a pure bend notched specimen of strain hardening material. The cleavage fracture load and cleavage fracture stress predicted using the model are in good agreement with the experimental results.MST/954

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.9.913

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractBy modifying 13Cr–4Mn (wt-%) white cast iron with boron and rare earth (RE)–Si complex, the carbide morphology of the iron can be changed from interconnected, coarse clusters of rods into a parallel distribution of isolated, fine rods, and the impact toughness of the iron can reach 6–7×104J m−2. In a pin wear test, the relative abrasion resistance of the iron is 1·01 and in a repeated impact abrasive wear test it is 0·95, in comparison with 15Cr–3Mo cast iron. Thus, it is stated that modifying high Cr–Mn cast iron with boron and RE–Si complex is very cost effective, and has almost the same abrasion resistance, when compared with 15Cr–3Mo cast iron.MST/957

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.9.918

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractAlloy IN 6201 satisfies the requirement for an alloy as strong as IN 792 with the corrosion resistance of IN 939, for investment cast blades in advanced industrial and marine gas turbines. Alloy IN 6203 was developed to optimise the combination of creep rupture strength and hot corrosion resistance available in directionally solidified blades for marine gas turbines. Following an outline of the basis for selecting the compositions of these alloys, data are provided on foundry characteristics, mechanical properties, corrosion resistance, alloy stability, and the result of trial casting of blades in IN 6201.MST/904

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.9.925

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe successful production of wide bimetallic sheets and strips by cold roll cladding depends on the technical solution of reduction of rolling load while still guaranteeing good bond quality. In the present paper, systematic experimental data on the cold roll cladding of aluminium–stainless steel, copper–stainless steel, and mild steel–stainless steel are correlated and the basic mechanism is discussed, aided by a scanning electron microscopy study of the separated interface. The effects of conventional rolling and cross-shear rolling (i.e. between rolls of differing peripheral speeds) on roll force and bonding strength are critically compared. It is found that use of the cross-shear cold rolling technique results in a significant reduction in rolling load for equal primary bonding strength and that the incorporation of an optimum final heat treatment considerably decreases the requirement on rolling.MST/971

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.9.934

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe deformation behaviour of different types of inclusion in the secondary shear zone of the chip and at the tool/chip interface has been studied during turning of quenched and tempered steel SS 2541 (En 24, SAE 4337) using coated carbide inserts. Inclusion types typical for both untreated and calcium treated steel were analysed. The analysis of inclusions in the secondary shear zone was based on semiautomatic image analysis in a scanning electron microscope. The influence on tool wear and on the formation of protective layers on the tool surface are discussed for the different types of inclusion. Examples are given of worn cutting inserts after machining steels of different inclusion content.MST/937

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.9.940

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor