Effect of Nickel Addition and Porosity on Fracture Behaviour of Molybdenum Alloyed Powder Metallurgical Steel

The influence of solutes, namely cobalt, molybdenum, nickel and silicon, on the deformation and fracture behaviour of Armco iron has been studied. The J -integral method was used for the measurement of ductile initiation fracture toughness J IC . Although cobalt is seen to enhance significantly J IC of the starting material (Armco iron), molybdenum, nickel and silicon are observed to have a deleterious effect. The increase in J IC with cobalt addition can be understood in terms of the enhanced strain hardening exponent, which is known to have a bearing on the plastic zone size around the crack tip and on micromechanisms of crack initiation. The large decrease in J IC with silicon and higher molybdenum concentration is explained on the basis of a change in fracture mode from ductile to cleavage as a result of stress concentration ahead of the crack tip reaching the cleavage fracture stress. The loss in fracture toughness with nickel addition is attributed to sulphur segregation at grain boundaries which results in pockets of intergranular fracture. Cobalt addition leads to alloy softening. Through secondary ion mass spectroscopy (SIMS), experimental evidence has been obtained for the first time for the suggestion that the ‘scavenging’ of interstitials leads to alloy softening. It was observed through yield stress dependence on grain size that the Hall–Petch constants σ 0 and k y substantiate SIMS observations.

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Microstructure of mechanically alloyed and hot-pressed Al5CuZr2

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100177982 ◽

1990 ◽

Vol 48 (4) ◽

pp. 970-971

Author(s):

T. E. Mitchell ◽

P. B. Desch ◽

R. B. Schwarz

Keyword(s):

Mechanical Alloying ◽

Vickers Hardness ◽

Hot Pressing ◽

Rapid Quenching ◽

Hardened Steel ◽

Alloyed Powder ◽

Ion Milling ◽

Mechanical Grinding ◽

Mechanically Alloyed ◽

Steel Container

Al3Zr has the highest melting temperature (1580°C) among the tri-aluminide intermetal1ics. When prepared by casting, Al3Zr forms in the tetragonal DO23 structure but by rapid quenching or by mechanical alloying (MA) it can also be prepared in the metastable cubic L12 structure. The L12 structure can be stabilized to at least 1300°C by the addition of copper and other elements. We report a TEM study of the microstructure of bulk Al5CuZr2 prepared by hot pressing mechanically alloyed powder.MA was performed in a Spex 800 mixer using a hardened steel container and balls and adding hexane as a surfactant. Between 1.4 and 2.4 wt.% of the hexane decomposed during MA and was incorporated into the alloy. The mechanically alloyed powders were degassed in vacuum at 900°C. They were compacted in a ram press at 900°C into fully dense samples having Vickers hardness of 1025. TEM specimens were prepared by mechanical grinding followed by ion milling at 120 K. TEM was performed on a Philips CM30 at 300kV.

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Mesoscale Modelling of Concretes Subjected to Triaxial Loadings: Mechanical Properties and Fracture Behaviour

Materials ◽

10.3390/ma14051099 ◽

2021 ◽

Vol 14 (5) ◽

pp. 1099

Author(s):

Qingqing Chen ◽

Yuhang Zhang ◽

Tingting Zhao ◽

Zhiyong Wang ◽

Zhihua Wang

Keyword(s):

Mechanical Properties ◽

Tensile Stress ◽

Failure Criterion ◽

Mesoscale Model ◽

Fracture Behaviour ◽

Descent Method ◽

Triaxial Stress ◽

Gradient Descent Method ◽

Stress States ◽

Shear Failures

The mechanical properties and fracture behaviour of concretes under different triaxial stress states were investigated based on a 3D mesoscale model. The quasistatic triaxial loadings, namely, compression–compression–compression (C–C–C), compression–tension–tension (C–T–T) and compression–compression–tension (C–C–T), were simulated using an implicit solver. The mesoscopic modelling with good robustness gave reliable and detailed damage evolution processes under different triaxial stress states. The lateral tensile stress significantly influenced the multiaxial mechanical behaviour of the concretes, accelerating the concrete failure. With low lateral pressures or tensile stress, axial cleavage was the main failure mode of the specimens. Furthermore, the concretes presented shear failures under medium lateral pressures. The concretes experienced a transition from brittle fracture to plastic failure under high lateral pressures. The Ottosen parameters were modified by the gradient descent method and then the failure criterion of the concretes in the principal stress space was given. The failure criterion could describe the strength characteristics of concrete materials well by being fitted with experimental data under different triaxial stress states.

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