Reinforced Tungsten Matrix Composites

Metal matrix composites (MMCs) have attracted more and more attention, and their reinforcements are generally particles, whiskers (or short fibers) and fibers. Metal matrix composites have higher specific strength, specific stiffness and high temperature strength than their matrix alloys. The preparation methods mainly include powder metallurgy sintering method and casting method (injection moulding).

Recently, some scholars have added composite carbide particles to tungsten matrix to form composite carbide particles reinforced tungsten matrix composites, in which tungsten is the matrix. The dopants can be Na, K and other elements. In addition, a small amount of dispersed particles such as ThO₂, HfC and YO₃ can be added to tungsten to form dispersion strengthening. The steps of strengthening tungsten matrix composites are as follows:

1.The composite carbide 4TaC.ZrC powder with particle size of about 2-3 micron and purity of over 98% is proportioned with tungsten powder with average particle size of about 3.5 micron and purity of over 99% according to volume percentage: 4TaC.HfC:W=30:70.

2.The mixture of composite carbide powder and tungsten powder is uniform, the mixing mode is wet mixing, the mixing medium is ethanol, acetone, etc. The steel ball or ceramic ball (alumina ball or zirconia ball, etc.) can be added to improve the mixing efficiency. The mixing powder and mixing medium are put in plastic cylinder or steel cylinder for mixing, and the mixing time is 2-36 hours.

3.Mixing and then drying in the drying oven, evaporating the mixture of ethanol or acetone, removing steel balls or ceramic balls, etc. 4. Mixing uniform powder, first cold pressing at room temperature, then hot pressing sintering, or direct hot pressing sintering without cold pressing, sintering temperature is 1900 ~2300 ℃, pressure mode is single. Pressure is 15-45 MPa, sintering holding time is 0.5-5 hours, and sintering atmosphere is hydrogen, argon, nitrogen or vacuum.

The above method can be used to make some parts in ultra-high temperature environment with weak oxidizing atmosphere and short working time. It can also be used to make some parts in reduction atmosphere or vacuum environment, such as high temperature die, fixture, etc. The density of tungsten-based metal composites is 90-95%. The flexural strength measured by three-point bending method at room temperature is about 700 MPa, the fracture toughness tested by edge-notched beam method is 9 MPa m1/2, and the three-point bending strength of composites at 1000 ℃ is about 800 MPa. The tensile strength at 1200 ℃ is greater than 300 MPa.

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