Optimization of deep penetration laser welding of thick stainless steel with a 10kW fiber laser

Material removal operations play a pivotal role in the manufacture of key components, required for engineering systems to operate safely and efficiently under ever more advanced functional requirements and over extended life cycles. To further step up the loading capability of machined parts, fundamental understanding of how of machining-induced features can influence the performance of advanced materials under complex service conditions is necessary over finer temporal and spatial scales. As discussed in Part I of this review, when engineering surfaces are generated by material removal processes, a wide range of physical mechanisms (e.g. mechanical, thermal, chemical and their combinations) drive the characteristics of workpiece surface integrity. In Part II of this review, the interplay between the metallurgical and micro-mechanical condition induced by material removal processes and their in-service response will be thoroughly explored, by a critical analysis of the state-of-the-art in the field. Specifically, attention is focused on recent advances made towards the understanding of the mechanisms determining the resistance of machined surface to fatigue crack nucleation (Section 2), corrosion and stress-corrosion cracking (Section 3), and wear (Section 4). Furthermore, the impact of relevant post-machining treatments on the in-service behaviour of machined surfaces is analysed, and the possible strategies for the enhancement of the functional performance of machined surfaces are presented (Section 5). Finally, the current research gaps and the prospective challenges in understanding the in-service behaviour of machined surfaces are critically discussed, providing an interpretation of the possible directions of future scientific development of this field.

Surface integrity in metal machining - Part II: Functional performance

Effect of Laser Shock Peening on surface properties and residual stress of Al6061-T6

Cold expansion technology of connection holes in aircraft structures: A review and prospect

Additive manufacturing (AM) technology has rapidly evolved with research advances related to AM processes, materials, and designs. The advantages of AM over conventional techniques include an augmented capability to produce parts with complex geometries, operational flexibility, and reduced production time. However, AM processes also face critical issues, such as poor surface quality and inadequate mechanical properties. Therefore, several post-processing technologies are applied to improve the surface quality of the additively manufactured parts. This work aims to document post-processing technologies and their applications concerning different AM processes. Various types of post-process treatments are reviewed and their integrations with AM process are discussed.

/pdf/a-review-of-post-processing-technologies-in-additive-48qgj0clha.pdf

A Review of Post-Processing Technologies in Additive Manufacturing

The effects of residual stress on fatigue behavior and crack propagation from laser shock processing-worked hole

The aim of the study was to investigate the influences of laser shock processing (LSP) on residual stress relaxation and metallographic structure evolution of 6061-T651 aluminum alloy at elevated temperature (up to 500 °C). Residual stress was determined by XRD with sin2ψ method, optical microscopy and TEM observations of the grain, and precipitated phase evolutionary process after LSP were carried out. The results showed that the effects of temperature on residual stress relaxation could be described, and the residual stress relaxation was analyzed precisely using the Zener–Wert–Avrami function. The main mechanism of stress relaxation between 200 °C to 300 °C was the dislocation slip and dislocation climb, and dynamic recovery was the main mechanism during the stress relaxation deformation between 400 °C to 500 °C. The evolution mechanism of grain and precipitated phase of 6061-T651 aluminum alloy between 25 °C and 500 °C was proposed. LSP still had a beneficial effect on residual stress at the elevated temperature 300 °C. Laser shock processing was the principal element for inducing the “metallographic variation” (MV) effect of 6061-T651 aluminum alloy at the elevated temperature.

Metallographic structure evolution of 6061-T651 aluminum alloy processed by laser shock peening: Effect of tempering at the elevated temperatures

The invention discloses a method for prolonging life of pump shells and blades by carrying out laser strengthening, which relates to the technical fields of machinery manufacturing and laser processing application. The method adequately combines the characteristics of laser cladding with laser shock strengthening, i.e., the method comprises the steps of performing laser cladding repair on micro-cracks at first, and then performing laser shock strengthening treatment on a cladding layer, thus effectively solving the problem that the pump shells and blades are easy to generate internal defects such as cracks and air holes in the laser cladding repair process, and avoiding the problems of welding deformation, large heat influence area, easy generation of heat cracks and the like in a conventional processing method; the method disclosed by the invention is capable of generating a high-amplitude residual compressive stress on the surface of a material, effectively improving the fretting fatigue resistance of the material, comprehensively improving the mechanical properties of the material, and greatly prolonging the fatigue life of the material, thus achieving the purposes of prolonging the life and improving the reliability and safety.

Method for prolonging life of pump shells and blades by carrying out laser strengthening micro-cracks

The effects of tempering on surface topography and dislocation configuration of 6061-T651 aluminum alloy by laser shock processing (LSP) were investigated at the elevated temperatures. Surface topography and surface roughness were tested by a Surfcom 130A-Monochrome surface rough-meter. Morphologies of precipitated phases were monitored by scanning electron microscopy (SEM), and the dislocation configurations of samples after LSP were characterized by transmission electron microscope (TEM). The results showed that LSP had a beneficial effect on micro-hardness at elevated temperature. There was a little change of the surface roughness as subjected to LSP. The main strengthening mechanism of micro-hardness was dislocation strengthening and fine grain strengthening, and precipitated phase strengthening was the main strengthening mechanism at elevated temperature. “Dislocation polymorphism transformation” (DPT) effect was affirmed at elevated temperature, and the elevated temperature was principal element for inducing the DPT effect of 6061-T651 aluminum alloy by LSP.

Dislocation polymorphism transformation of 6061-T651 aluminum alloy processed by laser shock processing: Effect of tempering at the elevated temperatures

The invention relates to a method and device for preparing a diamond-like carbon coating by cladding a carbon nanotube with fiber laser. The carbon nanotube is cladded with a fiber laser; the carbon nanotube is molten quickly by absorbing laser energy to form liquid carbon, and is cooled at an extremely high cooling speed; a diamond core grows, and undergoes phase change within an extremely short period of time; a part of carbon nanotube phases turn into diamond phases; the slightly-molten surface layer of a substrate material undergoes molecular level and atomic level diffusion, so that a strong metallurgically-bonded diamond-like carbon coating is formed; unbalanced condensation is led by an extremely high cooling speed; and an obtain diamond structure is fine and is approximate to a nanostructure. A used fiber laser head is coaxially connected with a powder spray head; processing is performed in a vacuum cavity; a laser beam is fully superposed with a carbon nanotube beam; and preparation of diamond-like carbon coatings of any shape and three-dimensional processing can be performed in cooperation with a flexible processing system of a six-degree-of-freedom robot.

Liang Ruan

Papers

The effects of residual stress on fatigue behavior and crack propagation from laser shock processing-worked hole

Metallographic structure evolution of 6061-T651 aluminum alloy processed by laser shock peening: Effect of tempering at the elevated temperatures

Method for prolonging life of pump shells and blades by carrying out laser strengthening micro-cracks

Dislocation polymorphism transformation of 6061-T651 aluminum alloy processed by laser shock processing: Effect of tempering at the elevated temperatures

Method and device for preparing diamond-like carbon coating by cladding fiber laser