Yimin Li

Dual‐phase titanium alloys are widely employed as ultrasonic waveguide materials for medical applications. However, the mechanisms underlying the interaction between microstructure and ultrasonic propagation in the alloy remain unclear. Herein, variations in the ultrasonic attenuation behavior of medical extra‐low‐interstitial‐grade Ti6Al4V alloys with microstructure evolution are systematically investigated. Experimental results demonstrate that within a d (grain size)/ λ (wavelength) range of 0.1–1, scattering attenuation and dislocation damping are the key factors affecting ultrasonic attenuation. Longitudinal‐wave scattering attenuation is directly proportional to the grain size, and dislocation damping is primarily influenced by the orientation of α grains. In particular, dislocation slip on the prismatic planes of α grains is found to be a key factor influencing the dislocation‐damping effect for dual‐phase Ti alloys. This can be attributed to the oscillatory movement of dislocations in response to ultrasonic‐wave disturbance when the wave propagation direction is parallel to the prismatic planes of α grains, causing energy dissipation. Further, the mechanisms by which dislocation types and movement patterns influence ultrasonic attenuation are discussed in detail based on a G–L dislocation pinning model.

The metal injection molding (MIM) method was applied to manufacture a shaped charge liner (SCL) used for petroleum perforating bombs. Its application could overcome the drawback of heterogeneous density distribution prepared using the traditional powder metallurgy and spinning process. The sintering results showed that because of the limitation in the sintering temperature, the relative density of the W–Cu alloy shaped charge liners prepared by metal injection molding (MIM W–Cu SCLs) ranged from 48.05% at 1050 °C to 52.52% at 1100 °C, which was far below those prepared by spinning. Further increase to higher temperature led to the W–Cu separation, cracks, and distortion of the SCL. The explosive test proved that the shaped charge liners prepared by metal injection molding (MIM SCLs) could achieve comparable or even better penetration performance than those prepared by spinning. The particle size of tungsten played a significant role in the penetration performance in which the sample prepared from a −250-mesh tungsten powder showed the highest penetration depth, which was 18.44% deeper than that of the spinning process. From the observation of ballistic holes, the jet of the MIM SCL was composed of dispersed W–Cu particles without a slug. The diameters of the holes bored by the MIM SCLs were larger than those SCLs produced by spinning, which proved that the MIM SCL jet is noncoherent.

At present, FeMn-based degradable alloys prepared by direct sintering generally face the problems of Mn volatilization, difficult densification, and poor mechanical properties. In this work, a Fe-35Mn-0.5C alloy with low Mn volatility, high density, and favorable mechanical properties is fabricated by the metal injection molding (MIM) process. The effects of sintering pressure and minor carbon addition on microstructure and mechanical properties were studied. The corresponding mechanical deformation mechanism was discussed. The results show that a significant reduction in the proportion of Mn volatilization to less than 0.5% and higher relative density of 97 ± 0.30% are achieved in the MIM-treated Fe-35Mn-0.5C alloy by pressurized sintering at 5 atm and 0.5 wt.% carbon addition. The optimized tensile properties are attained, with an ultimate tensile strength of 772 MPa, yield strength of 290 MPa, and elongation of 35% at room temperature, which meets the mechanical needs of metallic materials for biologically implantable medical devices.