TIG arc additive manufacturing experiments were performed utilizing TiB2 nanoparticle-reinforced toward to 7075 aluminum alloy welding wire, and the microstructure and mechanical properties corresponding to different locations of welding plate were investigated. At the top location of the deposited layer, the microstructure was characterized by fine dendrite induced by solidification, and equiaxed grain was predominant at the middle location. The grain size at the bottom location was obviously larger compared to the top and middle locations, and secondary-phase particles were homogeneously distributed at the grain boundary or inner grains. The mechanical properties at the top location of the deposited layer were most excellent compared to the middle and bottom locations, and the tensile properties and micro-hardness were decreased with the detected area varying from middle location to the bottom location. The excellent combination of fracture elongation and maximum of tensile strength corresponding to different locations on the deposited layer were determined to be 361.8 MPa with respect to the 7075 aluminum alloy welding wire, respectively, which was higher compared to the samples processed by general arc additive manufacturing process with tensile strength of (279.4 ± 5.3) MPa, indicating the TiB2 nano-sized particles possessed certain enhancing effects on the investigated 7075 aluminum alloy.

The wheel of high-speed trains requires high strength and hardness while imposing high demands on plasticity and toughness, resulting from the needs of working conditions. The fracture toughness KQ, as an important indicator of dynamics, often varies in the wheel, which affects the overall performance of the wheel. This work performs tests and analyses on typical samples with large fracture differences in fracture toughness at the same position and uniformly distributed on the same wheel. The mechanism of fracture toughness fluctuation is investigated, and the factors affecting fracture toughness are identified. The test mainly focuses on macroperformance, microfracture morphology, inclusion category and shape influence, pearlite lamellar spacing, and pearlite block size. Optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD), and quantitative metallographic technology were employed to investigate the mechanism and influence factors on fracture toughness fluctuation. The analysis shows that the width of the ductile laceration zone is directly correlated with the toughness, and the toughness level is influenced by the cleavage size, pearlite lamellar spacing, and pearlite block uniformity.

When maximum speed of 160 km/h is reached and the axle load reaches 25–30 tons, the train wheels need to have high strength and toughness. The main chemical elements affecting the strength and toughness of the wheel were determined by the mechanical features of the samples with different chemical compositions. Through analysis of the impact fracture of typical specimens, the difference of wheel toughness was mainly reflected in the dimple band, crack source, and cleavage pattern. By SEM analysis of fracture cracks, the critical size difference was found to exist between the grains during brittle fracture, where the intergranular fracture between grains of different sizes is mainly due to the different interfacial stresses between grains of different sizes.