Disclosed herein, in certain embodiments, are composite materials, methods, tools and abrasive materials comprising a tungsten-based metal composition, a tungsten carbide, and an alloy. In some cases, the composite materials or matrix are resistant to oxidation.

A method for friction stir forming a metal matrix composite (MMC) structure (76). The method includes the step of providing a substrate (12) comprising a metallic material and securing a preformed MMC layer (14, 16) comprising an MMC material in a position overlying at least a portion of the substrate (12). The method further includes the step of friction stirring the preformed MMC layer (14, 16) with a friction stirring tool (50) which includes a rotating probe (56), including locating the probe (56) at a stirring depth at which the probe (56) extends through the preformed MMC layer (14, 16) into a portion of the substrate (12) and passing the tool (50) through the preformed MMC layer (14) at the stirring depth to friction stir the preformed MMC layer (14, 16) and integrate the preformed MMC layer (14, 16) with the substrate (12).

Undercooled liquid metallic core-shell particles, whose core is stable against solidification at ambient conditions, i.e. under near ambient temperature and pressure conditions, are used to join or repair metallic non-particulate components. The undercooled-shell particles in the form of nano-size or micro-size particles comprise an undercooled stable liquid metallic core encapsulated inside an outer shell, which can comprise an oxide or other stabilizer shell typically formed in-situ on the undercooled liquid metallic core. The shell is ruptured to release the liquid phase core material to join or repair a component(s).

Ternary chromium-molybdenum-aluminum (CrMoAl) alloys that form oxidation-resistant surface films for high-temperature applications are provided. Also provided are methods for thermally pre-treating the alloys to form the oxidation resistant surface films. The surface films have a stratified structure that includes an exterior surface oxide layer comprising chromium oxides and aluminum oxides and an interior aluminum nitride-rich region comprising aluminum nitride precipitates dispersed in a CrMoAl alloy matrix. The interior aluminum nitride precipitates act as oxygen sinks to sequester oxygen diffusing inward into the CrMoAl to prevent further oxidation of the underlying bulk alloy.