Excimer laser surface treatment of plasma sprayed alumina-13% titania coatings

Surface modification of engineering materials allows the production of far superior products in terms of reduced wear, increased corrosion resistance, better biocompatibility, and improved optical and altered electrical/electronic properties. Excimer laser annealing provides a rapid and efficient means for surface alloying and modification of ceramic materials. In this study, alumina-13% titania (AT-13) coatings were sprayed with a water-stabilized plasma spray gun. The coated surface was treated by excimer laser having a wavelength of 248 nm and pulse duration of 24 ns. The surface structure of the treated coating was examined by field emission scanning electron microscope and X-ray diffraction (XRD). A detailed parametric study was performed to investigate the effects of different parameters such as laser energy density (fluence), pulse repetition rate (PRR), and number of pulses on the mechanical properties, surface morphology, and microstructure of the coatings. The study reveals that the laser fluence plays a major role in modifying the surface morphology of the coating, followed by the pulse repetition rate.     

Knowledge discovery for friction stir welding via data driven approaches

Abstract

For a comprehensive understanding towards friction stir welding (FSW) which would lead to a unified approach that embodies materials other than aluminium, such as titanium and steel, it is crucial to identify the intricate correlations between the controllable process conditions, the observable internal process variables, and the characterisations of the post-weld materials. In Part 1 of this paper, multiple correlation analyses techniques have been developed to detect new and previously unknown correlations between the internal process variables and weld quality of aluminium alloy AA 5083. Furthermore, a new exploitable weld quality indicator has, for the first time, been successfully extracted, which can provide an accurate and reliable indication of the as welded defects. All results relating to this work have been validated using real data obtained from a series of welding trials that utilised a new revolutionary sensory platform called ARTEMIS developed by TWI Ltd, the original inventors of the FSW process.     

An analytical model to calculate the peak temperature for friction stir welding

The peak temperature and temperature profile greatly affect the defect formation and the joint strength during the friction stir welding processing. An analytical model is proposed and tested to estimate the peak temperature based on the common constitutive equation of inverse hyperbolic sine function and the fundamentals of continuum mechanics. The calculated results of the peak temperature are consistent with the literature data of several aluminium alloys.     

Using permanent magnets for preventing magnetic arc blow in repair of transmission gas pipelines

The activities of The Welding Institute (TWI) in Cambridge (UK) are aimed at manufacturing industry with particular attention to joining technologies and the study of surface treatments, fields of strategic research with potentially high added value. Since the first ‘cross-flow’ LASERS for processing fine materials to more recently developed welding processes, TWI has produced innovations which have found important industrial applications, in some cases creating entirely new market sectors.

One of the best known technologies patented by TWI in recent years is ‘friction stir’ welding (FSW). This technology has particularly revolutionized the welding of aluminium and has had a great influence in industrial sectors such as aerospace and automobiles. This paper describes the most recent development in the FSW process, LASER and electron beam welding technologies, the experimental results obtained and various industrial applications.     

Alternative current flux zoned tungsten inert gas welding process for aluminium alloys

Abstract

A new variant of activating flux tungsten inert gas (TIG) welding process called flux zoned TIG (FZ-TIG) welding is proposed to weld aluminium alloys based on the mechanism of activating flux constricting welding arc. This process can not only increase weld penetration but also obtain perfect weld surface appearance simultaneously. An alternative current FZ-TIG welding is made using SiO₂ as the side region material and flux FZ108 developed by the authors with uniform design method as the central region coat material. The weld penetration can reach above three times that of the conventional alternative current TIG welding. All the weld shape, weld microstructure and weld mechanical properties are fine. Except for argon shielding gas flowrate, other welding parameters, including welding current, welding speed, central coat width, central coat content and solvent, have great effect on the weld penetration of alternative current FZ-TIG welding for aluminium alloys.     

Development of gap sensing system for narrow gap laser welding

Narrow gap welding with an oscillation laser beam is one of the effective processes for thick plate welding. To put this welding process into practical manufacturing, a groove-sensing system using image processing for narrow gap welding with an oscillation laser beam is used. This developed system uses still images of the weld zone taken by a coaxial CMOS camera. It can recognize the position of the groove wall by analysing the brightness distribution in the still image. It can then control the oscillation width and the laser-irradiated area by calculating the groove width and the groove centre position. Some narrow gap welding experiments were performed to evaluate the performance of the developed system. The results revealed that the developed system is effective for narrow gap welding with an oscillation laser beam. Using this system, the narrow gap groove can be welded even if the groove width has changed during the welding process.     

Design and characterisation of an advanced duplex system based on carbon S-phase case and GiC coatings for 316LVM austenitic stainless steel

Low temperature plasma carburising of austenitic stainless steels is attracting special attention because it can effectively improve their hardness, wear resistance and fatigue properties by the formation of interstitial supersaturated, super-hard and metastable S-phase. However, this S-phase layer tends to have a high friction coefficient between 0.5 and 0.7 under dry sliding conditions against WC ball. In this study, a new duplex surface system has been designed by combing chromium doped carbon-based GiC coating with S-phase to improve the tribological and load bearing capacity of 316LVM austenitic stainless steel. Laser confocal microscopy, SEM, XRD, XTEM, Micro-scratch and a pin-on-disc tester were employed to characterize the phase constitution, surface morphology, hardness, friction coefficient and load-bearing capacity of the single coated and duplex treated specimens. The results show that the new duplex surface system possesses a desirable combination of properties in terms of low friction (0.1-0.2), high wear resistance and high load bearing capacity.     

钨极氩弧焊熔池表面高度测量系统纵向标定

研究基于傅里叶变换轮廓术的钨极氩弧焊熔池表面高度测量系统的纵向标定方法,将一正弦光栅投向置于熔池位置的标定板,用一维精密移动装置带动平板纵向移动,构造不同的已知高度分布.4f系统把标定板上的光栅条纹转移到输出面,在输出面放置白屏接收输出图像,CCD拍摄屏上的光栅条纹,通过数字图像处理求出像素平面每点的位相值,确定系统的位相高度映射关系,对测量系统进行纵向标定并进行焊接实验,初步获得了熔池的表面高度分布.