An analysis of intergranular segregation of sulphur in a low alloy steel by stress-induced diffusion process
TL;DR: In this article, the influence of applied tensile stress on intergranular segregation of sulphur in 2.6NiCrMoV low alloy steel was investigated and it was determined from the ready applicability of grain boundary segregation isotherms, recorded for isothermally aged low alloy steels under unstressed and stressed conditions.
About: This article is published in Scripta Materialia.The article was published on 1996-09-15. It has received 8 citations till now. The article focuses on the topics: Coble creep & Alloy steel.
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TL;DR: In this article, a review of the literature on embrittlement of copper and its alloys is presented, showing how its occurrence can be rationalised in simple terms on the basis of what is known of intergranular creep fracture and dynamic recrystallisation.
Abstract: Copper and its alloys generally display a severe reduction in ductility between roughly 300 and 600 degrees C, a phenomenon variously called 'intermediate temperature embrittlement' or 'ductility trough behaviour'. This review of the phenomenon begins by placing it in the wider context of the high-temperature fracture of metals, showing how its occurrence can be rationalised in simple terms on the basis of what is known of intergranular creep fracture and dynamic recrystallisation. Data in the literature are reviewed to identify main causes and mechanisms for embrittlement, first for pure copper, and then for monophase and multiphase copper alloys. Coverage then turns to the 'grain boundary embrittlement' phenomenon, caused by the intergranular segregation of even minute quantities of alloying additions or impurities, which appears to worsen dramatically the intermediate temperature embrittlement of copper alloys. Finally, metal-induced embrittlement, including in particular liquid metal embrittlement, is presented as a second mechanism leading to an exacerbation of the intermediate temperature embrittlement of copper and its alloys.
65 citations
25 Aug 2006-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: Xu et al. as discussed by the authors showed that the segregation of phosphorus during stress-ageing has a non-equilibrium characteristic, i.e. it is not equilibrium segregation, and they used T.D. Xu's kinetic model for stress-induced grain boundary segregation.
Abstract: Grain boundary segregation of phosphorus under a 40 MPa tensile stress at 520 °C in a 0.025 wt.% P-doped 2.25Cr1Mo steel, which has already been thermally equilibrated, is examined using Auger electron spectroscopy. The segregation of phosphorus during stress-ageing has a non-equilibrium characteristic, i.e. it is non-equilibrium segregation. The segregation level first increases with increasing stress-ageing time until about 0.5 h and then diminishes with further increasing stress-ageing time, leading the boundary concentration of phosphorus to return to its thermal equilibrium value after ageing for about 15 h. Therefore, the critical time for this non-equilibrium grain boundary segregation of phosphorus is about 0.5 h at which the segregation is peaked. At this critical time, the boundary concentration of phosphorus is about 20.5 at.%, which is about 4.5 at.% higher than its thermal equilibrium level. Xu's kinetic model for stress-induced grain boundary segregation [T.D. Xu, Philos. Mag. 83 (2003) 889–899; T.D. Xu, B.-Y. Cheng, Prog. Mater. Sci. 49 (2) (2004) 109–208] is used to analyse the experimental results, demonstrating that the measured data may be well simulated by the model.
28 citations
15 Feb 2010-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the influence of phosphorus on the microstructure and stress-rupture properties of IN783 alloy, the newly developed low thermal expansion superalloy, was investigated.
Abstract: The influence of phosphorus on the microstructure and stress-rupture properties of IN783 alloy, the newly developed low thermal expansion superalloy, was investigated. Addition of phosphorus markedly promotes the precipitation of β-NiAl phase which improves the intergranular oxidation resistance of high P-doped alloys. However, phosphorus segregation deteriorates the interfacial cohesion of intergranular β/γ matrix and induces many intergranular cracks. Consequently, the stress-rupture life is reduced in high P-doped alloys.
22 citations
DOI•
01 Jan 2005
TL;DR: In this paper, the dihedral angle of intergranular lead inclusions is derived for high-purity Cu-1 wt.% Pb alloys with room temperature characterization.
Abstract: Mechanisms responsible for the embrittlement of leaded "free-machining" copper alloys at intermediate temperatures (i.e. around 400 °C) are examined using a combination of microstructural and mechanical characterization. Tensile tests are conducted on pure copper and on industrial high-strength Cu-Ni-Sn alloys, comparing leaded and unleaded versions, at strain rates ranging from 10-4 to 10 s-1, and various temperatures between 25 °C and 800 °C. It is found that, in the leaded samples, both liquid metal embrittlement and grain boundary embrittlement operate at intermediate temperature,i.e., near the melting point of lead. Their respective importance depends mainly on the strain rate: fracture at high strain rate (10 s-1) displays characteristic signatures of liquid metal embrittlement, while at low strain rate (10-4 s-1) the ductility trough behaviour can be attributed to grain boundary embrittlement. In leaded copper and copper alloys, lead is mostly present as discrete inclusions, frequently located along grain boundaries. The dihedral angle of intergranular lead inclusions is then the main microstructural parameter besides their size. A new technique is proposed and demonstrated for the measurement of inclusion dihedral angle in a high-purity Cu-1 wt.% Pb alloy, based on room temperature characterization of samples that were held at elevated temperature at times sufficiently long for shape equilibration of the inclusions and then rapidly quenched. Quantitative scanning electron microscopic analysis of metallographic surfaces along which individual inclusions have been dissolved is used to deduce the dihedral angle using a mathematical fit of their solid/liquid interface. For a specific temperature, we show that the dihedral angle is not unique; this reflects the fact that high-angle grain boundary energies are not constant in copper. Existing micromechanical analyses of shape equilibrium for intergranular inclusions in the presence of external stress are adapted to produce an improved description at low stress and to take into account the inclusion bulk compressibility. The derivation is based on minimization of the global capillary and elastic strain energy associated with such inclusions. An adimensional parameter that depends on the applied stress, the inclusion volume, the elastic properties of the solid, and the relevant interfacial energies emerges from the analysis as the sole factor governing the shape of the inclusion. If void nucleation occurs easily within the inclusion, such that its apparent bulk modulus is nil, the inclusion become unstable, degenerating to a crack when this adimensional parameter exceeds a critical value. Measurements of the dihedral angle on samples previously subjected to a remote stress at 400 °C show that applied stress causes a reduction in the apparent dihedral angle of liquid lead inclusions. Calculated critical stresses for both leaded pure copper and leaded copper-nickel-tin alloys that fail at high strain rate by liquid metal embrittlement are calculated for individual inclusions in the metal. These calculated critical stresses correlate relatively well with the measured fracture stress, suggesting that shape instability of the inclusions cause fracture of the alloys. This result is applied towards the suggestion of general strategies for reduction of the susceptibility of leaded copper alloys to liquid metal embrittlement. A case study addressing the problem of quench cracking of leaded Cu-Ni-Sn alloys on the basis of experimentation and finite element thermomechanical simulation, showing how the problem can be alleviated in production, concludes the thesis.
14 citations
TL;DR: In this article, an extended program of basic research at the author's current and former institutions to understand the part played by crystal structure, solute additions, grain size, grain boundary chemistry, texture, and substructural features such as retained austenite, martensite lath, and packet size, and characteristics of other microstructural constituents.
Abstract: High strength-high toughness combination and formability has been the primary focus of the author's research over the last two decades, where the attempt was to either develop newer steels or maximize the fracture resistance of engineering steels at specified levels of strength. In this regard, significant success was achieved based on an extended program of basic research at the author's current and former institutions to understand the part played by crystal structure, solute additions, grain size, grain boundary chemistry, texture, and substructural features such as retained austenite, martensite lath, and packet size, and characteristics of other microstructural constituents. Each of these features influences the fracture mode, the degree of plasticity, and the rate of growth of nucleated voids. Important instances include maraging steels, precipitation hardened stainless steels, low alloy steels, interstitial-free steels, microalloyed steels, pipeline steels, and silicon-containing medium carbon stee...
11 citations
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TL;DR: In this article, it was suggested that the zirconium hydride precipitate acts as a marker, and that magnesium atoms diffuse into the grain boundaries that lie at right angles to the applied stress.
94 citations
60 citations