Undulation of W/matrix interface by resintering of cyclically heat-treated W-Ni-Fe heavy alloys

Lee

Song

1999

Metall Mater Trans A

Self Cite

The effect of the size and shape of tungsten particles on dynamic torsional properties in tungsten heavy alloys was investigated. Dynamic torsional tests were conducted on seven tungsten alloy specimens, four of which were fabricated by repeated sintering, using a torsional Kolsky bar, and then the test results were compared via microstructure, mechanical properties, adiabatic shear banding, and deformation and fracture mode. The size of tungsten particles and their hardness were increased as sintering temperature and time were increased, thereby deteriorating fracture toughness. The dynamic torsional test results indicated that in the specimens whose tungsten particles were coarse and irregularly shaped, cleavage fracture occurred predominantly with little shear deformation, whereas shear deformation was concentrated into the center of the gage section in the conventionally fabricated specimens. The deformation and fracture behavior of the specimens having coarse tungsten particles correlated well with the observation of the in situ fracture test results, i.e., cleavage crack initiation and propagation. These findings suggested that there would be an appropriate tungsten particle size because the cleavage fracture mode would be beneficial for the "self-sharpening" of the tungsten heavy alloys.

Section: Methodsmentioning

confidence: 99%

“…Thus, homogethose under repeated sintering are changed to irregularly neous deformation will give way to a localized bandlike shaped from spheroidal. [18] Dynamic torsional tests were deformation mode. This is an adiabatic shear band.…”

Section: Introductionmentioning

confidence: 99%

Effect of size and shape of tungsten particles on dynamic torsional properties in tungsten heavy alloys

Lee

Song

1999

Metall Mater Trans A

Self Cite

“…There have been some studies reporting that such an irregular morphology is also observed in the cases of repeated heat treatment after sintering, or of resintering after deformation processing [14,22]. Particularly, in the D specimen fabricated with repeated sintering of 20 times, particles are sized up to about 75 Bm with their shape becoming extremely irregular.…”

Section: Microstructurementioning

confidence: 97%

“…This indicates that hardness of particles has a tendency to rise as particles become larger as a result of increasing the number, time, and temperature of sintering, although matrix hardness is almost the same, irrespective of repeated sintering. This can be explained by the formation of interfaces inside tungsten particles caused by the increased number of resinterings [14]. Rockwell hardness, which means overall bulk hardness, descends in the order of the A-S, B-S, and C-S specimens as sintering time becomes longer, and resintered A-R, B-R, and C-R specimens show slightly higher hardness over the A-S, B-S, and C-S specimens.…”

Section: Microstructurementioning

confidence: 99%

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Effect of size and shape of tungsten particles on penetration performance in tungsten heavy alloys

Lee

Song

1999

Metals and Materials

Self Cite

The effects of the size and shape of tungsten particles on dynamic torsional properties in tungsten heavy alloys were investigated. Dynamic torsional tests were conducted on seven tungsten alloy specimens, four of which were fabricated by repeated sintering, using a torsional Kolsky bar, and then the test results were compared via microstructure, mechanical properties, adiabatic shear banding, and deformation and fracture mode. The size of tungsten particles and their hardness were increased with the increasing of the sintering temperature and time, thereby deteriorating the fracture toughness. The dynamic torsional test results indicated that a cleavage fracture occurred predominantly with little shear deformation in the specimens whose tungsten particles were coarse and irregularly shaped whereas shear deformation was concentrated into the center of the gage section in the conventionally fabricated specimens. The deformation and fracture behavior of the specimens having coarse tungsten particles correlated well with the observation of the in situ fracture test results, i.e., cleavage crack initiation and propagation. These findings suggested that there would be an appropriate tungsten particle size condition in the penetration performance since the cleavage fracture mode would be beneficial for the self-sharpening of tungsten heavy alloys.

The effect of managanese addition on the microstructure of W-Ni-Fe heavy alloy

Baek

Moon

1999

Metall Mater Trans A

The influence of Mn addition on the growth kinetics and morphology of W grains in W-Ni-Fe heavy alloy has been studied. The addition of Mn was performed by placing a compact of Mn powder on the sintered specimens containing constant Ni/Fe ratio of 8/2 but different W contents of 93 and 97 wt pct followed by resintering. The sintering and resintering treatments were carried out at a temperature of 1485 ЊC under a dry hydrogen atmosphere. The addition of Mn leads to the deviation of growth rate of W grains from the diffusion-controlled Ostwald ripening: the growth rate is initially enhanced and then decayed. The difference in the average grain radius between the alloys containing high and low W contents is decreased by the addition of Mn. The cause of the change in the growth rate of W particles with the addition of Mn is discussed in terms of the competitive soluble reactions of Mn and W atoms. The addition of Mn also results in the morphological change of W grains from roundish to angular shape. The addition of Mn into the matrix phase, which is artificially made, forms the dendritic W grains. From these results, it is found that the morphological change of W grains is closely related to the precipitation reaction of W atoms on the preferred orientation.