Wire and Arc Additive Manufacturing (WAAM) was used for fabrication of NiTi parts using a commercialy available Ni-rich NiTi wire as the feedstock material. The as-built parts are near fully austenitic at room temperature as confirmed by differential scanning calorimetry, X-ray diffraction and superelastic cycling. The as-built microstructure changed from collumnar, in the first deposited layers, to equiaxed in the last deposited ones as a result of the different thermal cycle conditions. This is the first work where WAAM NiTi parts exhibit superelastic behavior under tensile conditions, highlighting the potential use of the technique for the creation of parts shaped in a complex manner based on this material and process. The potential to use WAAM for deposition of advanced functional materials is demonstrated.

Wire and arc additive manufacturing of a Ni-rich NiTi shape memory alloy: microstructure and mechanical properties

Power ultrasound and its applications: A state-of-the-art review.

Agricultural water resources have been limited over the years due to global warming and irregular rainfall in the arid and semi-arid regions. To mitigate the water stress in agriculture, mulching has a crucial impact as a water-saving technique in rain-fed crop cultivation. It is important mainly for preserving soil moisture, relegating soil temperature, and limiting soil evaporation, which affects the crop yield. Mulching has many strategic effects on soil ecosystem, crop growth, and climate. Mulch insulates the soil, helping to provide a buffer from cold and hot temperatures that have a crucial activity in creating beautiful and protected landscapes. This study has accumulated a series of information about both organic and plastic mulch materials and its applicability on crop cultivation. Moreover, future research potentials of mulching with modeling were discussed to quantify water loss in agriculture.

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Mulching as water-saving technique in dryland agriculture: review article

Hot-wire arc additive manufacturing of aluminum alloy with reduced porosity and high deposition rate

https://hal.archives-ouvertes.fr/hal-01289332/document

Microstructure and residual stresses in Ti-6Al-4V alloy pulsed and unpulsed TIG welds

Based on 0Cr18Ni9Ti austenitic stainless steel plate (h = 6 mm), a study on arc behavior by ultrasonic frequency pulse gas tungsten arc welding (GTAW) process has been carried out. The results show that with the increasing pulse frequency, an obvious pinch effect of arc plasma has been detected and also the increment of arc voltage, stiffness, and force. Then, the method, combining weld appearance and numerical simulation, has been adapted for weld behavior on the basis of arc behavior by ultrasonic frequency pulse GTAW process. As a result of arc shrinkage, the root radius of arc decreased, which caused narrower weld bead. The larger arc force led to more depression of pool surface that made the downward heat source and external force point, which had been important to increasing weld penetration. Meanwhile, the mobility of molten pool was enhanced by weld behavior compared with conventional GTAW process.

The effect of arc behavior on weld geometry by high-frequency pulse GTAW process with 0Cr18Ni9Ti stainless steel

Effect of arc behavior on Ti-6Al-4V welds during high frequency pulsed arc welding

An experimental program of welding a titanium alloy, Ti-6Al-4V, was carried out using ultrahigh-frequency pulse gas tungsten arc welding (UHF-GTAW). The characteristics of the welds were investigated, such as the defection, microstructure, and mechanical properties. The experimental results show that the high pulse frequency reduces the heat input from the UHF-GTAW process, while gaining one-side welding with backing as a precondition. Basketweave and long acicular α′ martensite only existed in some areas of the FZ (fusion zone) with both low uniformity and distribution density (8.4 %) as a result of conventional GTAW processes. With a pulsed current, basketweave and short acicular α′ martensite were distributed in the FZ evenly. Short acicular α′ martensite could be detected within the parallel long acicular α′ martensite in the CGR when f > 30 kHz. Plastic weld joints were characterized by both the elongation, A, and the percentage of the area reduction, Z, and were optimized with a high pulse frequency. Ideal mechanical properties of the joints were achieved with an A of 68 % and a Z of 150 % with f = 30 kHz. The integrated effects of the pulse frequency and the heat input are the key factors for determining the microstructure morphology and the mechanical properties.

Effect of pulse frequency on microstructure and properties of Ti-6Al-4V by ultrahigh-frequency pulse gas tungsten arc welding.

Microstructure, tensile properties of Ti-6Al-4V by ultra high pulse frequency GTAW with low duty cycle

Ultra high frequency of pulsed gas tungsten arc welding (UHFP-GTAW) has been considered as a promising method to improve weld quality of titanium alloys. This paper studies the effect of UHFP-GTAW on weld porosity of Ti-6Al-4V alloy, which shows how liquid pressure/viscosity/temperature of molten pool influences nucleation, growth, detaching, and escaping of gas pore. Results indicated that compared to conventional GTAW, the liquid pressure and curvature radius of the gas pore were increased significantly while viscosity and filtration angle of the gas pore reduced simultaneously caused by UHFP-GTAW, leading to high escaping speed and easy detaching process of the weld gas pore. It is suggested that the elimination of weld porosity of Ti-6Al-4V alloy can be achieved by UHFP-GTAW process.

Mingxuan Yang

Papers

The effect of arc behavior on weld geometry by high-frequency pulse GTAW process with 0Cr18Ni9Ti stainless steel

Effect of arc behavior on Ti-6Al-4V welds during high frequency pulsed arc welding

Effect of pulse frequency on microstructure and properties of Ti-6Al-4V by ultrahigh-frequency pulse gas tungsten arc welding.

Microstructure, tensile properties of Ti-6Al-4V by ultra high pulse frequency GTAW with low duty cycle

How ultra high frequency of pulsed gas tungsten arc welding affects weld porosity of Ti-6Al-4V alloy