The production method of tantalum-10Tungsten rods involves preheating a tantalum-10Tungsten ingot, coating its surface with an anti-oxidation coating, then heating the coated ingot sequentially at power levels of 20KW~40KW and 60KW~80KW. The heated ingot is then forged, undergoing radial upsetting and radial drawing, repeated multiple times. Finally, the forged ingot is annealed to obtain the tantalum-10Tungsten rod. Compared with existing technologies, this invention, through graded heating with different heating powers, can effectively reduce the generation and concentration of residual internal stress in the ingot caused by excessively rapid temperature gradients and heating rates. In terms of forging, radial upsetting and drawing methods are used to fully break down the columnar crystal regions in the center and core of the ingot, increasing the circumferential flow of metal in the columnar crystal regions of the ingot's center, thereby significantly improving the inhomogeneity of the as-cast microstructure of the tantalum-10tungsten ingot. Furthermore, through repeated forging, the presence of undesirable microstructures such as dendrites, crystal bands, non-equiaxed crystals, and coarse grains in the as-cast tantalum-10tungsten ingot is eliminated, while simultaneously refining the grain and strengthening the material, thus preventing localized deformation and cracking failure of the tantalum-10tungsten rod under high-temperature and high-pressure conditions.
Preheating the tantalum-10tungsten ingot first facilitates the bonding of the anti-oxidation coating on the ingot surface with the ingot substrate surface. As is well known to those skilled in the art, tantalum enters a relatively active oxygen absorption temperature at 180°C. Therefore, the preheating temperature is preferably 120-180°C to avoid the initial active oxygen absorption temperature. As is well known to those skilled in the art, there are two methods of heating metals: furnace heating and temperature-to-furnace heating. Due to tantalum's strong chemical reactivity and gas absorption properties, furnace heating exposes the tantalum-decatungsten ingot to oxygen in an environment for an extended period, leading to oxidation. As a preferred embodiment, this invention uses temperature-to-furnace heating to preheat the tantalum-decatungsten ingot. This method rapidly raises the ingot surface temperature within a short time, while reducing gas absorption and oxidation during heating. The preheating time is preferably 20-40 minutes, more preferably 25-35 minutes.
After preheating the tantalum-decatungsten ingot, an anti-oxidation coating is applied to its surface. Applying an anti-oxidation coating to the surface of the tantalum-decatungsten ingot prevents oxidation of the ingot substrate and inhibits further diffusion of oxygen atoms into the ingot. The anti-oxidation coating is preferably a suspension of water, water glass, and high-temperature glass powder. The thickness of the anti-oxidation coating is preferably 2-3 mm.
After coating the surface of the tantalum-10-tungsten ingot with the anti-oxidation coating, the resulting tantalum-10-tungsten ingot is heated. This invention employs medium-frequency induction heating, heating the tantalum-10-tungsten ingot coated with the anti-oxidation coating sequentially at 20-40 kW and 60-80 kW. To more effectively reduce the residual internal stress of the ingot, as a preferred embodiment, step c) specifically involves: placing the tantalum-10-tungsten ingot coated with the anti-oxidation coating in a medium-frequency induction coil, heating sequentially at 20 kW for 4-6 minutes, at 40 kW for 5-7 minutes, at 60 kW for 8-12 minutes, and at 80 kW for 10-12 minutes. During the heating process, to strictly control the heating temperature, this invention preferably uses a high-temperature infrared thermometer for monitoring, ensuring that the temperature difference from the center to the edge of the cross-section is no greater than 20°C, and the overall radial temperature difference of the ingot is no greater than 40°C. The preferred heating temperature is 1350-1400°C. This invention employs a staged heating method with different heating frequencies, which contrasts with fixed-frequency heating. Fixed-frequency heating results in a rapid heating rate, a high temperature gradient, and a high degree of internal stress concentration, making the forging process prone to cracking at stress concentration points and failure due to crack propagation. Staged heating with different frequencies, however, has a lower heating rate and a lower temperature gradient, reducing the likelihood of internal stress concentration and effectively decreasing the possibility of cracking during forging.
The tantalum-tungsten ingot, after being heated, is then forged. As is well known to those skilled in the art, the ingot is melted in an electron beam furnace in the radial direction, i.e., along the length of the ingot. Radial melting is the direction in which coarse grains, dendrites, and grain bands are formed, and this direction also exhibits better plasticity. Radial upsetting can break down the coarse grains and dendrites in the cast state radially, refining the grain structure. Simultaneously, radially upset ingots are easier to deform and less prone to cracking. Repeated upsetting and elongation, that is, repeatedly compressing and elongating the cast dendrites and coarse grains along the orientation of the microstructure, is extremely beneficial for breaking down the cast microstructure, effectively refining the grains. If forging is completed in a single radial upsetting and elongation cycle, the microstructure cannot be effectively refined and strengthened, failing to achieve the desired microstructure effect. This invention involves radial upsetting and elongation of the heated ingot, ensuring thorough breaking down of the columnar crystal regions in the center and core of the ingot. This increases the circumferential flow of metal in the columnar crystal regions at the center of the ingot, thereby significantly improving the inhomogeneity of the cast microstructure of the tantalum-tungsten ingot. In this invention, the forging process can proceed either radial upsetting followed by radial elongation, or vice versa; there are no particular limitations on this. However, according to this invention, single-stage upsetting or single-stage elongation is not permitted.
