Matrix Penetration of W/W Grain Boundaries and Its Effect on Mechanical Properties of 93W-5.6Ni-1.4Fe Heavy Alloy

et al. 2001

Metall Mater Trans A

The objective of this study is to investigate the dynamic deformation and fracture behavior of an oxide-dispersed (OD) tungsten heavy alloy fabricated by mechanical alloying (MA). The tungsten alloy was processed by adding 0.1 wt pct Y 2 O 3 powders during MA, in order to form fine oxides at triple junctions of tungsten particles or at tungsten/matrix interfaces. Dynamic torsion tests were conducted for this alloy, and the test data were compared with those of a conventional liquid-phase sintered (LPS) specimen. A refinement in tungsten particle size could be obtained after MA and multistep heat treatment without an increase in the interfacial area fraction between tungsten particles. The dynamic test results indicated that interfacial debonding between tungsten particles occurred over broad deformed areas in this alloy, suggesting the possibility of adiabatic shear-band formation. Also, oxide dispersion was effective in promoting interfacial debonding, since the fine oxides acted as initiation sites for interfacial debonding. These findings suggest that the idea of forming fine oxides would be useful for improving self-sharpening and penetration performance in tungsten heavy alloys.

Section: Figures 9(a) Through (D) Are a Series Of Sem Micrographsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dynamic deformation behavior of an oxide-dispersed tungsten heavy alloy fabricated by mechanical alloying

Park

Kim

et al. 2001

Metall Mater Trans A

“…Since they provide cracking sites and facilitate the crack propagation, they deteriorate the overall properties. In addition, these boundaries can deter the formation and propagation [28].…”

Section: Discussionmentioning

confidence: 99%

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

Kim

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 interface between gains and the softer Ni-Fe-W matrix is strong; however, the tungsten-tungsten grain boundaries are relatively weak and a cyclic heat-treatment between the usual heat-treatment temperature and water quenching has recently been found able to reduce the W/W grain boundary area in tungsten heavy alloys [7,8]. The result of the cyclic heat treatment is the placement of the matrix between the W/W grain boundary and a drastic increase in impact energy.…”

Section: Cyclic Heat Treatmentmentioning

confidence: 99%

Analysis of strengthening mechanisms through cyclic heat treatment of tungsten heavy alloys

2000

Metals and Materials

A cell model is presented and numerical analyses are implemented to find the distribution of thermally induced stress, thermally induced deformation and the effect of the tungsten volume fraction during a single step of the quenching process for a 2-dimensional cell model and to find the strengthening mechanisms through the cyclic heat treatment of tungsten alloys. The thermal stresses induced from a single step of quenching mostly concentrated on the W/matrix interface and W/W grain boundary region and the stresses were distributed locally in tensile and locally in the compressible state both in matrix and particle. The mechanism of matrix phase formation at tungsten-tungsten boundaries during cyclic heat-treatment was found to be due to the combination effect of the super saturated matrix phase precipitation into W/W grain boundaries and the thermal stresses state. These results enhance the impact energy enhancement in tungsten heavy alloys.