Effect of layer thickness on crack suppression in laser engineered net shaping of ceramic structure

Laser engineered net shaping (LENS) has been innovatively applied to direct additive manufacturing of ceramics in recent years. Using this technique, neat ceramic powder without binders can be completely melted and solidified, obtaining compact and high-purity netshaped ceramic structures rapidly. However, existing LENS process for fabricating ceramics suffers from cracking defect due to intrinsic brittleness of ceramics and high temperature gradient in deposition. Here we reported the effect of layer thickness on cracking in LENS of ceramic structure, which indicates that cracks can be effectively suppressed by reasonably optimizing process parameters. Pure Al2O3 structures with different layer thickness were fabricated by LENS system and their microstructure were analyzed to figure out the crack suppressing mechanism of optimizing layer thickness. Results indicate that cracks of fabricated specimen decreases obviously with the increase of layer thickness. Reduction of grain boundary defects and increase of transverse grain ratio are the main mechanism of crack suppression.Published versio

Microstructure and Wear Resistance of TiCp/Ti6Al4V Composite Coatings by Follow-Up Ultrasonic-Assisted Laser Additive Manufacturing

With the increasing demand for the high agility and fast response of high-level equipment in the aerospace and energy power fields, it is increasingly urgent to improve the performance of the high-temperature and wear resistance of the corresponding high-level components. Ceramic-reinforced titanium matrix composites have excellent high-temperature and wear resistance, but, in laser additive manufacturing, the primary ceramic phase is coarse, and the morphology of the ceramic phase is difficult to control, which limits their further development. In this investigation, a follow-up ultrasonic-assisted laser-additive-manufacturing method was proposed to prepare a 30 wt.% TiC/Ti6Al4V composite coating on a Ti6Al4V surface. Under the effects of ultrasonic cavitation and acoustic streaming, the content of the unmelted TiC was reduced, the dendritic primary TiC in the solidification process was broken and the distribution uniformity of the primary TiC was improved. The content of the unmelted TiC in the composite coating decreased significantly under ultrasonic action, and it was only 50.23% of that without ultrasonic action. At the same time, the average size of the dendritic primary TiC in the composite coating decreased from 61.59 μm to 27.04 μm, which was 56.10% smaller than that without ultrasonic action. The average microhardness of the composite coating reached the maximum of 656.70 HV0.2 under ultrasonic power, and it was 83.21% higher than that of the Ti6Al4V substrate, and 26.44% higher than that of the composite coating without ultrasonic power. Due to the ultrasonic-cavitation and acoustic-streaming effects, the content of the unmelted TiC obviously decreased, so that the average friction coefficient of the composite coating increased, and the wear mechanism changed from abrasive wear to adhesive wear

Research progress in additive manufacturing of melt growth ceramics by laser directed energy deposition

Melt growth ceramics (MGC) is a new type of ceramic material with microstructure obtained by melting and solidification of raw materials. The clean and high-strength bonding interface shared by atoms makes it have excellent high-temperature mechanical properties and microstructure stability close to the melting point. It shows great application potential in the field of high thrust weight ratio aero-engine and heavy gas turbine hot end components in the future. Laser directed energy deposition (LDED) technology can effectively overcome the limitations of traditional preparation methods of MGC in terms of cycle, energy consumption and structural complexity. It provides a new solution for direct additive manufacturing of MGC components, and has become a research hotspot at home and abroad. Based on the introduction of the process principle of LDED technology, the microstructure characteristics and properties of different MGCs prepared by this technology at home and abroad were summarized in this paper, and the main research on the control of microstructure and cracking behaviour was comprehensively discussed. Based on the existing research progress, the development trend and key scientific problems to be further solved in this field were discussed. It was pointed out that inhibiting cracking and improving microstructure and properties are the primary problems faced at present. The development of materials and new processes is the key to breaking through the existing bottleneck and promote the development and application of MGC-LDED

Effects of TiO2 Doping on Microstructure and Properties of Directed Laser Deposition Alumina/Aluminum Titanate Composites

10.1080/17452759.2019.1622987Virtual and Physical Prototyping144371-38

Effect of post-deposition heat treatment on laser-TIG hybrid additive manufactured Al-Cu alloy

After solution + artificial aging treatment (T6 heat treatment) of 2219 aluminum alloy fabricated by laser-tungsten inert gas (TIG) hybrid method, more interestingly, we found that both the strength and elongation were improved. The strengthening mechanism has been analysed in details. Results showed that each layer was divided into the arc zone (AZ) and laser zone (LZ) before and after heat treatment. After T6 heat treatment, the columnar crystal grain morphologies remained the same as the as-deposited condition, while the microstructure presented a strong {001} texture along the building direction. Moreover, the high density of the needle-shaped θ″ phases were uniformly precipitated after artificial aging. Distinct grain morphology, increased the mass fraction of Cu in the Al matrix, and nano-precipitates in the AZ and LZ improved the tensile properties, which exhibited a yield strength of 242.1 ± 19.6 MPa, an ultimate tensile strength of 407.1 ± 31.1 MPa, respectively