Based on the single screw extruder, straw/PLA composites with different straw mass fraction, drawing temperature and screw speed were prepared with corn straw powder and PLA particles as raw materials, and FDM printing test was carried out to further study the influence of straw mass fraction, drawing temperature and screw speed on the mechanical properties of straw/PLA composites The results show that the tensile strength of the composite is the best when the straw content is 15%, the drawing temperature is 215°C, the screw speed is 60r/min; the flexural strength of the composite is the best when the straw content is 15%, the drawing temperature is 215°C, the screw speed is 70r/min; the hardness of the composite is the best when the straw content is 10%, the drawing temperature is 195°C, the screw speed is 70r/min.

A comprehensive study was carried out to investigate the effects of Fe addition (0–0.9 wt.%) on the microstructure evolution and mechanical properties of Ti-6Al-4V alloys. The results indicate that Fe addition has a significant refinement effect on the microstructure of titanium alloys; specifically, 0.9 wt.% Fe addition can lead to a 47.37% decrease in the width of lamellar α. The modulus also decreases by 18.89% with the increase in the Fe content, being 91.40 GPa in Ti-6Al-4V-0.9Fe. And the microhardness and wear resistance are improved due to Fe addition. In addition, the constitutive equation of the Fe content and the elastic compliance coefficient were calculated, which can better describe the relationship between Fe addition and the elastic–plastic properties of titanium alloys. The slip systems’ activity during the deformation process was also discussed using the Schmid factor. It shows that Fe addition is beneficial for the activity of prismatic and pyramidal slip systems, especially in the {10$\overline{1}$0} , {10$\overline{1}$1} , and {11$\overline{2}$2} slip systems.

The titanium matrix composites (TMCs) fabricated via Directed Energy Deposition (DED) effectively overcome the issue of coarse columnar grains typically observed in additively manufactured titanium alloys. In this study, systematic annealing heat treatments were applied to in situ (TiB + TiC)/Ti-6Al-4V composites to refine the microstructure and tailor mechanical properties. The results reveal that the plate-like α phase in the as-deposited composites gradually transforms into an equiaxed morphology with increasing annealing temperature and holding time. Notably, when the annealing temperature exceeds 1000 °C, significant coarsening of the TiC phase is observed, while the TiB phase remains morphologically stable. Annealing promotes decomposition of acicular martensite and stress relaxation, leading to a reduction in hardness compared to the as-deposited state. However, the reticulated distribution of the TiB and TiC reinforcement phases contributes to enhanced tensile performance. Specifically, the as-deposited composite achieves a tensile strength of 1109 MPa in the XOY direction, representing a 21.6% improvement over the as-cast counterpart, while maintaining a ductility of 2.47%. These findings demonstrate that post-deposition annealing is an effective strategy to regulate microstructure and achieve a desirable balance between strength and ductility in DED-fabricated titanium matrix composites.

To address the anisotropy of mechanical properties and the challenge of removing support materials in lattice structures fabricated using fused deposition modeling (FDM), this study is inspired by traditional woodworking mortise and tenon joints. A hexagonal interlocking mortise lattice structure was designed, and mortise and tenon lattice structures (MTLSs) with various parameters were fabricated. Compared with the traditional integrated forming lattice structure (IFLS), the MTLS exhibits maximum reductions in side surface roughness (Ra), printing time, and material consumption of 74.87%, 25.55%, and 52.21%, respectively. In addition to enhancing surface quality and printing efficiency, the MTLS also exhibited superior mechanical properties. The uniaxial compression test results show that the specific strength, energy absorption (EA), and specific energy absorption (SEA) of the MTLS exhibit maximum increases of 51.22%, 894.59%, and 888.39%, respectively, compared with the IFLS. Moreover, the effects of strut angle and thickness on the lattice structure were analyzed. Smaller strut angles and larger strut thicknesses endowed greater strength, while smaller angles contributed to higher energy absorption. This study proposes a novel approach for designing lattice structures in additive manufacturing.

In this study, the newly developed Ti35421 (Ti3Al5Mo4Cr2Zr1Fe wt.%) alloy was prepared by laser directed energy deposition (L-DED) because it contains several major elements that can refine grains, which is expected to enable the transformation from columnar to equiaxed grains. The results show that the L-DED Ti35421 alloy is predominantly composed of equiaxed grains and features various α-phase morphologies, including grain boundary α, lath α, and acicular α′ structures. These microstructural features are attributed to the rapid cooling conditions during processing. Such a microstructure enhances the alloy’s tensile strength (1446 MPa) while leading to limited ductility (1.7%). Following the solution and aging treatment, the grain boundary α phase undergoes coarsening, while the matrix β phase transforms into numerous fine lamellar α phases. This leads to a reduction in strength but an improvement in ductility. Therefore, the optimal heat treatment process for the L-DED Ti35421 alloy is determined to be a two-stage procedure: first, heating at 780 °C for 2 h followed by air cooling, and subsequently heating at 575 °C for 8 h with air cooling. Under this treatment, the alloy exhibits excellent mechanical properties, including a tensile strength of 1196 MPa, a yield strength of 1162 MPa, an elongation of 6.8%, and a reduction in area of 16.7%. Since there are no continuous grain boundaries in α, the rolled Ti35421 alloy exhibits better ductility than the L-DED Ti35421 alloy. This article is a revised and expanded version of a poster presentation entitled “Microstructure and mechanical properties of Ti-3Al-5Mo-4Cr-2Zr-1Fe alloy fabricated by laser deposition manufacturing”, which was accepted and presented at the 15th World Conference on Titanium (Ti-2023), Edinburgh, UK, 12–16 June 2023.

Significant columnar grains usually occur in the metallurgical microstructure of laser additive manufacturing, and plastic deformation introduced into additive manufacturing can significantly refine grain size. Due to the high deformation resistance and difficult deformation of titanium alloys, reducing the high-temperature deformation resistance of additive manufacturing titanium alloys is essential to facilitating the implementation of online rolling processes. High-temperature compression of titanium alloys was performed on a Gleeble-3800. It was found that the flow stress of the alloy decreased when the strain of the alloy decreased or the deformation temperature increased. The flow behavior of titanium alloys at high temperatures was investigated with the help of a Z-parameter flow model and multiple linear regression model. A positive correlation was found between the experimental and predicted values of the alloy under the multiple linear regression model, with a correlation coefficient of 0.98 and its error of 13.5%, which could better predict the flow stress values. In addition, hot processing maps were established, and the optimal deformation conditions were determined to provide some theoretical guidance for subsequent experiments.