The equiatomic CoCrFeNiMn high-entropy alloy (HEA) possesses excellent properties including exceptional strength–ductility synergy, high corrosion resistance, and good thermal stability. Selective laser melting (SLM) additive manufacturing facilitates the convenient fabrication of the CoCrFeNiMn HEA parts with complex geometries. Here, the SLM process optimization was conducted to achieve a high relative density of as-built CoCrFeNiMn HEA bulks. The mechanisms of process-induced defects and process control were elucidated. The microscale mechanical behaviors were analyzed through in situ scanning electron microscopy observation during the compression tests on micro-pillars of the as-built HEA. The stress–strain characteristics by repeated slip and mechanism of “dislocation avalanche” during the compression of micro-pillars were discussed. The high-cycle fatigue tests of the as-built HEA were performed. It was found that a large number of nano-twins were induced by the fatigue, causing a non-negligible cycle softening phenomenon. The effects of promoted ductility due to the fatigue-induced nano-twins were illustrated. This work has some significance for the engineering application of the SLM additively manufactured CoCrFeNiMn HEA parts.

This paper presents a novel framework of hydraulic-driven biped robot. The target biped robot is a humanoid robot NWPUBR-1 with 12 degrees of freedom (DOF), and its dimensions are close to that of an average male. The joint axis adopts the modular structure design of sensor with angle measurement, and the force sensor is deployed on the side of hydraulic actuator to facilitate force and position control of the robot. Meanwhile, the finite element analysis of critical components is conducted to meet the requirements of mechanical strength in motion. Based on the screw theory, the forward kinematics and Jacobian matrix models are established, and the inverse kinematics of robot is solved by using the analytical geometric method. To achieve real-time control of the robot gait in 3D space, a three-dimensional linear inverted pendulum model (3D-LIPM) is built, and a 3D gait model is generated by combining the zero-moment point (ZMP) theory. In the virtual environment of MATLAB software, the results of programming simulation show that the biped robot can walk stably in the virtual environment, which proves the correctness of 3D-LIPM.

In this study, we comprehensively investigate the structure and operational principles of the Rotary Direct Drive Electro-Hydraulic Pressure Servo Valve (RDDPV). Our objective is to establish the dynamics equations governing the motor, slide valve, and bias mechanism of the valve. Additionally, we construct a mathematical model for the servo valve controller, while ensuring the linearization of the controller model. Furthermore, we conduct an in-depth analysis of the static characteristics of the valve, including linearity, dead zone, hysteresis loop, and zero drift. Regarding the dynamic characteristics, we establish a dynamic mathematical model for the RDDPV valve. Subsequently, we subject the servo valve to analysis with a focus on frequency response and dynamic response, using the control current as the input and the pressure as the output. To perform these analyses, we employ the software package SIMULINK of MATLAB, facilitating dynamic simulations. Remarkably, the simulation results exhibit the valve's conformity to design requirements, underscoring its suitability for subsequent research and development endeavors. Through our rigorous investigation, we offer essential technical support for the forthcoming stages of the valve's research and development, thereby laying a robust foundation for its further advancement.

Using pulsed double electrode-gas metal arc welding, aluminum wires are joined to copper plates with fillers of different fractions of silicon. Two layers of different microstructures are formed near the Al-Cu interface: one consists of a hypoeutectic microstructure of α (Al) + Al₂Cu, and the other consists of an intermetallic compound (IMC) of Al₂Cu. Increasing the heat input causes increases in the thicknesses of the IMC layer and the layer of the hypoeutectic microstructure. Si suppresses the growth of the IMC layer and assists the growth of the layer of the hypoeutectic microstructure. The effects of the interface microstructures and chemical compositions on the electric resistivity of the joints are analyzed. The electric resistivity of the joints increases with the increase in the thicknesses of the IMC layer and the layer of the hypoeutectic microstructure. The law of mixture is used to calculate the electric resistivity of the joints, which is in accordance with the experimental results.

Laser powder bed fusion (L-PBF) additive manufacturing technology is suitable for the direct 3D printing of geometrically complex periodic micro-rod-lattices. However, controlling the geometric and performance consistency remains challenging due to manufacturability limitations, non-negligible process defects, and surface roughness, which is inconvenient to measure, affecting the mechanical properties and deformation behavior of the lattice structures. To improve the forming quality of the rod lattices and the consistency of repetitive 3D printing, we theoretically analyzed the causes of the defects and the effects of the L-PBF parameters on the process defects of CoCrFeNiMn high-entropy alloy micro-rods. The forming quality of the micro-rods was evaluated and classified with control experiments, and the surface roughness was measured and analyzed. Randomly protruding metal particles on the surface were mainly caused by the diffusion of laser energy, the incomplete melting of some metal powders, and/or “balling” process-induced defects caused by laser remelting. The tensile mechanical properties of typical L-PBF-printed micro-rods with different geometric characteristics were compared and evaluated. The influence of the geometric characteristics of the defects on the mechanical properties is discussed. The mechanical properties of the L-PBF-printed rod lattices were evaluated by compression experiments. It was found that the properties of different rod lattices have a positive relationship with the relative density.