Research on Residual Stresses and Microstructures of Selective Laser Melted Ti6Al4V Treated by Thermal Vibration Stress Relief.

The efficient and cost-effective residual stress control method is of great significance for the application of additive manufacturing (AM) technology. In this work, thermal-vibration stress relief (TVSR) with different temperatures and dynamic stresses was performed on Ti6Al4V samples prepared by selective laser melting (SLM), the stress relief effects of TVSR and its influence on phase and microstructure were investigated and compared with thermal stress relief (TSR) and vibration stress relief (VSR), and the stress relief mechanisms of these methods are discussed. It was found that the residual stress relief rate can reach 86.76% after TVSR treatment at a temperature of 380 °C and a dynamic stress of 400 MPa, which increased by 63.63% compared with VSR under the same dynamic stress. The efficiency is increased by 76% compared with TSR at 580 °C and the residual stress relief rate is almost the same. After TVSR, VSR and TSR treatments, the grain morphology, size and phase content of samples were basically unchanged, and low-angle grain boundaries (LAGBs) were increased after TVSR and VSR treatments and decreased after TSR treatment. The results confirm that the TVSR method has the ability to control the residual stress of selective laser melted Ti6Al4V with low time and cost consumption, and are helpful for engineering applications of TVSR.

Reversely Orthogonal Actuation of a Janus-Faced Film Based on Asymmetric Polymer Brush Modification.

The actuation phenomena of materials upon external stimulus have attracted much attention for the development of excellent sensors and devices. Herein, we present a smart Janus-faced film that exhibits novel behavior of reverse orthogonal actuation under high humidity and a positive actuation under low humidity, which is achieved by asymmetric polymer brushes on polydimethysiloxane as a substrate through surface-initiated atom transfer radical polymerization. The classical theory of plates and shells and finite element simulations are also applied to understand the orthogonal actuation mechanism of the actuator. This Janus-faced film can reversely grab objects rapidly under high humidity, which provides significant potential to design a more intelligent actuator. In addition, this film is highly sensitive to humidity that even the approaching finger can make it to bend, which is just like the actuation behavior of Mimosa pudica. Based on the above phenomena, we also design the sensing devices to realize the detection of humidity. Interestingly, the film intelligently identifies different solvents (e.g., water and ethanol). This work may demonstrate significant potential in smart surface modifications, flexible robots, bionic sensors, and other fields.

Enhanced Wave Absorption and Mechanical Properties of Cobalt Sulfide/PVDF Composite Materials.

A cobalt sulfide/PVDF(Polyvinylidene Fluoride) composite was prepared by a simple blending method, and the microstructure of the composite was investigated through X-ray diffraction, scanning electron microscopy, and field emission scanning electron microscopy. Increased absorption properties at frequencies ranging from 2 GHz to 18 GHz were studied, and the mechanical properties were investigated via tensile tests and finite element method simulations. The results indicated that the cobalt sulfide/PVDF composites exhibited strong microwave absorption intensities (-43 dB at 6.6 GHz) with a low filler loading (5.0 wt%). The elastic modulus increased with the cobalt sulfide mass fraction. Cobalt sulfide could improve the mechanical properties of the composite, especially in the lengthwise direction.