다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Revisiting fundamental welding concepts to improve additive manufacturing: From theory to practice

Ni-rich NiTi alloys were deposited using the in-situ alloying wire arc additive manufacturing (WAAM) method, with varying deposition currents from 80 A to 120 A. The effects of deposition current on the crystal orientation, precipitation, phase transformation and mechanical properties of the WAAM-deposited NiTi alloys were investigated. The results show that increasing the deposition current during the WAAM process would result in noticeable coarsening of B2 grain and an increased volume fraction of high angle grain boundaries (HAGBs). Also, the texture intensity gradually decreased with increasing deposition current. The fabricated components are dominated by the B2 phase with quantities of Ni4Ti3 precipitates in all samples. When increasing the deposition current during the WAAM process, the size of Ni4Ti3 precipitates generally increased and gradually decomposed into a stable Ni3Ti phase which could be detected in the sample produced at 120 A. Furthermore, all of the characteristic phase transformation temperatures increased with the deposition current while the ultimate tensile strength dropped from 927.9 MPa to 613.8 MPa and elongation reduced from 8.7 % to 5.6 %. The cyclic loading-unloading tests revealed that similar trends for the evolution of irreversible strain (eir), recoverable strain (ere), recovery ratio, and elastic energy storage efficiency (η) during cycling were obtained in all samples processed with different deposition currents. The highest ere of 3.2 % and the highest recovery ratio of 53.9 % were obtained in the sample processed with 80 A at an applied stress of 700 MPa for ten cycles. The change of mechanical properties with varying deposition current is due to a combination of factors including precipitation hardening effect, grain refinement effect, and crystal orientation. These results can be useful for optimizing WAAM process parameters to fabricate NiTi components with acceptable structural properties.

Evolution of crystallographic orientation, precipitation, phase transformation and mechanical properties realized by enhancing deposition current for dual-wire arc additive manufactured Ni-rich NiTi alloy

One of the less desirable aspects of fusion-based additive manufacturing is the propensity for coarse columnar grain structures crossing build layers to form This paper initially attempts to explain the reason for the formation of columnar grain structures in terms of the high thermal gradients typically observed during solidification and the alloy compositions that are typically used which promote epitaxial growth Successful approaches to the grain refinement of titanium alloys using alloying elements that produce constitutional supercooling are discussed along with the difficulty with nucleant additions Much of the grain-refining technology already used in aluminium casting is shown to also be applicable to additive manufacturing, although the novelty of the effective use of nanoparticles as nucleants is highlighted It is also shown that for other alloy systems for which there is a lack of grain-refining technology using chemical means, mechanical means, such as ultrasonic treatment, can be effective across a wide range of alloys Finally, consideration is given to the difficulties and the possible solutions of producing parts layer by layer In particular, the importance of understanding nucleation in solidification conditions characterized by high cooling rates and thermal gradients; the importance of melt dynamics; and how previous layers could provide possibilities for refinement of the subsequent layer are highlighted

/pdf/grain-refinement-of-alloys-in-fusion-based-additive-1j5tzo0k2a.pdf

Grain Refinement of Alloys in Fusion-Based Additive Manufacturing Processes

An attempt, combined with the technologies of laser cladding and laser remelting, has been made to develop a Ni-Cr-Co-Ti-V high entropy alloy coating. The phase composition, microstructure, micro-hardness and wear resistance (rolling friction) were studied in detail. The results show that after laser remelting, the phase composition remains unchanged, that is, as-cladded coating and as-remelted coatings are all composed of (Ni, Co)Ti2 intermetallic compound, Ti-rich phase and BCC solid solution phase. However, after laser remelting, the volume fraction of Ti-rich phase increases significantly. Moreover, the micro-hardness is increased, up to ∼900 HV at the laser remelting parameters: laser power of 1 kW, laser spot diameter of 3 mm, and laser speed of 10 mm/s. Compared to the as-cladded high-entropy alloy coating, the as-remelted high-entropy alloy coatings have high friction coefficient and low wear mass loss, indicating that the wear resistance of as-remelted coatings is improved and suggesting practical applications, like coatings on brake pads for wear protection. The worn surface morphologies show that the worn mechanism of as-cladded and as-remelted high-entropy alloy coatings are adhesive wear.

Microstructure and wear resistance of laser cladded Ni-Cr-Co-Ti-V high-entropy alloy coating after laser remelting processing

Effect of Wc Content on Microstructure and Properties of High-Speed Laser Cladding Ni-Based Coating

Microstructure and properties of ZrB2-SiC continuous gradient coating prepared by high speed laser cladding

Effect of in-situ synthesis of multilayer graphene on the microstructure and tribological performance of laser cladded Ni-based coatings

The microstructure of cerium-based conversion coatings with and without microcapsules containing Ce(NO3)3 or La(NO3)3 on magnesium alloys were investigated and the corrosion resistance was evaluate...

Self-healing conversion coating with gelatin–chitosan microcapsules containing inhibitor on AZ91D alloy

Today, many researchers focus on the destructive effects of the laser in underwater environment. In this paper, we present underwater wet laser repairing which is a kind of technique to avert the destructive effects of the interactions between laser, water and target. We introduce helpful materials to repair nickel aluminum bronze (NAB) plate and discuss the effect of interactions between the laser, water and target on the repairing quality during underwater wet laser repairing process. As a result, the useful materials, Zn and Ti, protect melting pool from damaging by the high-speed water jet and shock wave. The as-repaired layers possess good repairing quality. In addition, the as-repaired layer manufactured by underwater wet laser repairing process possesses smaller heat affected zone, smaller coating thickness and more deformation than the layer manufactured in the air. In summary, with the help of the useful materials, a good repairing quality can be obtained.

Effect of the protective materials and water on the repairing quality of nickel aluminum bronze during underwater wet laser repairing

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