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The present investigation highlights the creep deformation and rupture behavior of indigenously produced as-cast Mg-10 wt.%Sn-3 wt.%Al-1 wt.%Zn (TAZ1031) and Mg-10 wt.%Sn (T10) alloys. Conventional creep tests were conducted at 423 K (150 °C) in the stress range of 30-45 MPa and at 45 MPa in the temperature range of 423-453 K (150-180 °C) for both the alloys. The nature of creep curves was found to be identical for both the alloys with short primary and secondary creep regime, followed by extended tertiary creep region. The creep resistance of the TAZ1031 alloy was better than the T10 alloy. The former exhibited reduced minimum creep rate and enhanced creep rupture life under identical creep test conditions with respect to the latter. The change of minimum creep rate (έmin) followed a power-law relationship with a change in applied stress (σ) for both the alloys with a significant change in stress exponent (n) value. Activation energy for creep deformation of TAZ1031 alloy (~ 117 kJ/mol) was found to be higher than T10 alloy (~ 105 kJ/mol). Fine secondary Mg2Sn precipitates within the α-Mg matrix and primary Mg2Sn, Mg17Al12 and MgZn2 precipitates along the grain boundaries improved the creep properties of TAZ1031 alloy. On the contrary, the threshold stress required for creep deformation was found to be significantly low in TAZ1031 alloy due to the presence of Mg17Al12. Both creep damage analysis and dimpled fracture surfaces revealed necking dominated creep deformation for the alloys. SEM studies revealed the absence of creep cavities along grain/dendritic boundaries for the investigated alloys, which substantiated the formation of dimpled fracture surfaces during creep deformation. [ABSTRACT FROM AUTHOR]

Deformation characteristic of centrifugal casting 25Mn steel was investigated by compression tests, and then processing maps were established. According to the deformation parameters identified from the established processing maps and hot ring rolling (HRR) process, the industrial test for the 25Mn ring blank was performed. Optical microscope (OM) and electron backscatter diffraction (EBSD) techniques were used for detecting grain boundary features and textures of deformation structures. The morphologies and mechanisms of tensile and impact fracture were revealed. The results show that softening effect plays a dominant role in higher temperatures of 1050-1150 °C and strain rates lower than 0.1 s. The average grain size of the rolled 25Mn ring is about 28 μm, but the grains are more coarse and inhomogeneous on the middle layer than that on rest of the areas. The texture on the outer layer is characterized by strong {110} 〈112〉 and weak {112} 〈111〉, followed by {001} 〈100〉 and {001} 〈110〉 on the inner layer and {110} 〈110〉 on the center layer, which is mainly associated with the shear deformation. The rolled ring with precise geometrical dimensions and sound mechanical properties is fabricated by HRR. Tensile fracture is composed of clear river-shaped pattern and a little dimple near the inner layer and outer layer, and the fracture mechanism is mainly quasi-cleavage fracture, accompanied by dimple fracture. The morphologies of impact fracture consist of tear ridge and cleavage platform. [ABSTRACT FROM AUTHOR]

Abstract: A failure investigation has been conducted on the turbo-disk used in a locomotive turbochanger, which is made from GH2132 high-temperature alloy. The fracture of three teeth and the crack of 11 teeth took place, which mainly occurred at the third root near the groove. Fractographic studies indicate that the crack originated at the root and propagated along the turning direction of the turbo-disk. In the initial crack propagation zone several different failure mechanisms performed successively, which are the intergranular corrosion crack, the corrosion-fatigue propagation and the dimple fracture. The greater bending stress on the tooth root and the presence of the corrosion medium in the service circumstance should be responsible for the failure of the turbo-disk. [Copyright &y& Elsevier]

Dimple fracture mechanisms are discussed for three kinds of aluminum alloys on the basis of an experimental approach and a finite element (FEM) analysis. The void growth and coalescence process was observed by an optical microscope and a scanning electron microscope. The fractographic observation for aluminum alloys 7075-T651 and 6061-T651 showed that several large voids called a dominant void are nucleated at inclusion sites or the second-phase particles ahead of the crack tip and followed by fine voids initiation leading coalescence of the dominant voids with the crack tip. On the other hand, in aluminum alloy 2017-T3, voids are nucleated very close to the crack tip and directly coalesce with the crack tip. FEM computation results suggested that the void nucleation and growth process is closely related to the triaxial stress state ahead of the crack tip. [Copyright &y& Elsevier]

In this study, it is aimed to investigate the damage mechanisms of a DP1000 steel with very fine-grain microstructure and further study the effect of the stress states and loading rates on the damage mechanism. To ensure clear and systematic conclusions are drawn about the effect of stress state on the damage mechanism, careful study is performed on achieving a constant stress state of the fracture initiation spot during the entire deformation history by designing a fracture specimen family for various stress states. The specimens feature an identical dog-bone specimen layout with only differences at the detailed notches and cuts to ease the experimental and analysis effort. After testing the optimized fracture specimens from quasi-static to intermediate loading rates, the scanning electron microscopy is employed to analyze the damage mechanism of the investigated material. Both dimple and shear fracture modes are observed in DP1000 and the underlying damage mechanisms are ferrite-martensite interphase debonding and martensite cracking. By systemic analysis, it is found that the stress state and loading rate have distinct influences on triggering the dominant fracture mode and the underlying damage mechanism. Furthermore, the damage mechanism of DP1000 is compared with DP600 steel and significantly different behavior is observed for two types of dual-phase steels. Unlabelled Image • A set of fracture specimens is proposed for various local stress states under global uniaxial tension. • Distinct plastic strain is found for the central and surface elements for samples under various stress states. • Both ferrite–martensite debonding and martensite cracking are found to be the main damage mechanisms. • A clear correlation of the damage mechanisms with stress state is concluded. • Higher loading rate promotes shear fracture and inhibits dimple fracture. [ABSTRACT FROM AUTHOR]