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Titanium alloy powder injection molding vacuum degreasing sintering

Apply powder injection molding technology to prepare high-precision, high-performance special-shaped titanium alloy components. By mixing multi-granularity powders and using polyoxymethylene as the main component as a multi-component binder, a high-loading catalytic degreasing titanium alloy feed is prepared, and then the product is obtained through vacuum degreasing and sintering.

For powder injection molding technology, higher loading capacity helps to densify the product and is also a strong guarantee for obtaining high dimensional precision products. The higher the tap density, the easier it is to obtain high loading capacity.

Under the conditions of catalytic degreasing at a N₂ feed rate of 120 cm³·min⁻¹ and a temperature of 120 °C, the effect of HNO3 gas flow on degreasing efficiency (or weight loss rate) was studied by changing the HNO₃ gas feed rate. During the same degreasing time, the weight loss rates of the three samples increased with the increase of the HNO3 gas introduction rate. When the HNO3 gas introduction rate reaches 2.0cm³·min⁻¹, the weight loss rates of the three feed materials reach the maximum value within 6 h, that is, the POM in the binder is completely decomposed. When the HNO₃ gas introduction rate is 1.0 cm³·min⁻¹, it takes more than 6 hours to feed PB, PC, and PA to reach the peak, indicating that the too low HNO3 gas introduction rate causes the degreasing process to be slow. At the same time, as the powder loading increases, the weight loss rate decreases and the peak value also decreases slightly. This is because the higher the powder loading, the less POM is added.

It can be concluded that the catalytic degreasing efficiency (or weight loss rate) will increase as the acid gas introduction rate increases. This is because the increase in HNO₃ gas flow increases the concentration of HNO₃ in the catalytic degreasing furnace, which intensifies the depolymerization reaction of POM. When the HNO₃ gas introduction rate is too low, the degreasing time will be long and the degreasing efficiency will be low; when the HNO3 gas introduction rate is too high, although the degreasing efficiency will be significantly improved, the difficulty of tail gas treatment will also increase accordingly, and the acid gas concentration will be too high. Corrosion to equipment will increase. Comprehensive consideration, when the N₂ introduction rate is 120 cm³·min⁻¹ and the temperature is 120 °C, the appropriate HNO₃ gas introduction rate is 1.5 cm³·min⁻¹.

Conclusion on the application of vacuum degreasing and sintering

(1) Using multi-particle size powders can effectively increase the powder loading capacity. When the mass ratio of large (D50=25.28 μm), medium (D50=16.75 μm) and small (D50=12.66 μm) particles is 17:6:2 , the relative tap density of the mixed powder is larger, 55%.

(2) When the binder with polyformaldehyde (POM) as the main component is used to prepare the feed, the catalytic degreasing efficiency increases with the increase of the nitric acid gas flow rate and the degreasing temperature. When the degreasing temperature exceeds 120 At ℃, the changing trend slows down. The optimal catalytic degreasing process is a degreasing temperature of 120 ℃, an N₂ inlet rate of 120 cm³·min⁻¹, an HNO₃ gas inlet rate of 1.5cm³·min⁻¹, a degreasing time of 6 h, and a binder removal rate of 85%.

(3) Using technology to control impurity content throughout the process, the vacuum sintering performance of powder injection molded titanium alloy products can reach a relative density of 95.9%, a tensile strength of 933 MPa, a flexural strength of 1282 MPa, an elongation of 7.5%, and a C mass fraction of 0.10 %, O mass fraction 0.21%.