LASER SURFACE TREATMENTS FOR PROMOTING CORROSION RESISTANCE OF A CARBON STEEL

The effect of laser treatment and laser alloying on corrosion resistance of 1045 steel has been studied. Various ways of surface alloying have been investigated by using continuous CO₂ laser beam: i) irradiation of chromium painted surfaces; ii) irradiation of Ni and Cr-electroplated surfaces; iii) direct injection of Ni and Cr powders into the melt pool. A high and uniform level of alloying in the surface layer can be achieved in the cases of electroplated surfaces and direct powder injection. It requires, however, an appropriate choice of irradiation conditions (such as beam power, beam traverse speed, beam defocusing and degree of overlapping) that provide remelted layer of a limited and fairly uniform thickness. It has been found that in order to achieve corrosion behavior of laser treated surfaces similar to that of austenite type 304 stainless steel chromium and nickel contents in the alloyed layer are to be higher than those of 304 steel.     

激光扫描速度对40Ct钢激光表面合金化层组织性能的影响

为了改善金属拉拔卷筒40Cr铜的性能,采用Mo制成合金粉末,用CO2激光对卷筒表面进行激光合金化处理。研究激光合金化的工艺参数,对不同扫描速度下合金化层的质量进行比较并对其组织进行分析。结果表明：激光合金化工艺参数为：功率P=2．0kW,焦距f=315mm,搭接率为40％,扫描速度V=6mm／s,获得的合金化层具有良好的组织和性能,没有裂纹产生,未发现不熔物,组织较均匀。     

Distribution of concentration of gold in the process of laser alloying of the nickel surface layer

The paper presents the results of studies on the mechanism of laser alloying of nickel with gold. From the investigations carried out, it has been found that thermocapillary phenomena play a predominant role in the alloying process. Experiments have satisfactorily confirmed the distribution area of the capillary motion velocity obtained by theoretical calculations. The paper contains examples of the actual distribution of the alloying material concentration in the areas alloyed with a single laser pulse.     

Two step coating of a hypereutectic PM Al-Si alloy

The aim of the present work was to combine the high strength of Al-Si alloys produced via Rapid Solidification (RS) and Spray Forming (SF) with a wear resistant surface coating, designed for high temperature use. The surface coating, composed mainly of nickel and chromium, was applied in a two step process: plasma spray followed by laser surface alloying using a diode laser. The microstructure and hardness of the surface coating were analysed. In the Al-Si alloys produced via Rapid Solidification, gas bubble formation was observed during the laser alloying process. In the Spray Formed alloys, globules of the coating material and a needle-like microstructure formed, in detriment to the mechanical properties of the alloyed layer.     

Modification of metal surfaces by the laser melt-particle injection process

The laser melt-particle injection process was used to accomplish diverse modifications in the structure and chemistry of metal surfaces. This process consists in melting a shallow pool on the surface of a metal with a high power laser beam and injecting fine particles into the melt. In this paper we discuss wear-resisting surfaces produced by injecting TiC particles into the surfaces of 5052 aluminum and by surface alloying the same base metal with silicon. The operating conditions employed in the surface-alloying experiments were very similar to those used for carbide injection, but nearly complete dissolution of the injected silicon particles occurred during alloying while the injected carbide particles did not dissolve to any detectable degree.Previous experiments with this process have all been conducted at reduced pressure in an inert gas. The surface alloying and some of the carbide injection work described here were done at atmospheric pressure using a powder injection nozzle with inert gas shielding.     

The sintering process of a high permeability Ni-Fe-Cu-Mo alloy made by powder metallurgy

The magnetic permeability of a 77 Ni-14 Fe-5 Cu-4 Mo wt % alloy made by powder metallurgy is known to be improved by extending the sintering time considerably beyond that normally used. The room temperature measurement of resistivity during the sintering cycle of such an alloy clearly shows the overlapping stages of change that occur during the sintering process. The variation in resistivity and its relationship with the changes in density, in weight and in bend strength of compacts shows that de-oxidation of the constituent element powders occurs initially. De-oxidation is followed by sintering and alloying of the nickel and iron which is followed in turn by alloying of the molybdenum. The final stage involves the alloying of the copper and the elimination of pores.Electron microprobe analysis has shown that the copper does not alloy substantially until the copper particles melt, and that alloying is hindered if copper powder of large particle size is used. Sintering occurs more rapidly than alloying, but the rate of alloying is the most important factor in determining the electrical and magnetic properties of the alloy.     

合金化填充材料Ni 对SiCP/6061Al 复合材料激光焊接焊缝显微组织的影响

以N i 片作为合金化填充材料对SiC_P/6061A l 金属基复合材料(SiC_P/6061A lMMC) 进行激光焊接, 研究了激光输出功率、焊接速度等焊接工艺参数对焊缝显微组织的影响。结果表明, 采用金属N i 片作为合金化填充材料对SiC_P/6061A lMMC 进行激光焊接, 可以在一定程度上抑制SiC 颗粒的溶解及针状脆性相Al₄C₃ 的形成, 并获得以Al₃Ni 等相为增强相的焊缝显微组织, 但在焊缝心部有粗大的气孔形成。      

超级双相不锈钢2507焊接工艺研究现状

主要梳理和综述了超级双相不锈钢2507焊接方面的研究工作,从而对超级双相不锈钢2507焊接工艺进行指导。从超级双相不锈钢2507焊接工艺、焊接接头两相比例调节两个维度进行综述,其中,超级双相不锈钢2507焊接工艺部分从钨极氩弧焊、埋弧焊、等离子弧焊、激光焊、电子束焊、激光-电弧复合焊这6种焊接工艺开展评述,焊接接头两相比例调节部分从调整焊接热输入、焊后热处理、添加合金元素镍或氮3个方面进行评述。结合国内外研究现状,探讨了超级双相不锈钢焊接如何控制接头两相比例这一关键问题。研究现状表明:钨极氩弧焊、等离子弧焊和激光焊可以较好地实现超级双相不锈钢优质焊接;添加合金元素镍或氮是调控焊接接头两相比例的重要手段。开展超级双相不锈钢2507焊接工艺研究现状的综述具有重要意义,向熔池过渡合金元素的高能量密度焊接工艺可能是超级双相不锈钢焊接的优选技术。     

Structure and Corrosion-Mechanical Properties of the Surface Layers of Steels after Laser Alloying

We perform the thermodynamic analysis of the solubility of alloying elements and stability of possible secondary phases of chromium and chromium-nickel steels in the components of the Li₁₇Pb₈₃ eutectic heat carrier and reveal the negative effect of the lead melt on the long-term strength and plasticity of the major part of these steels. It is proposed to improve the stability of the characteristics of structural steels promising for nuclear and thermonuclear power engineering by the laser alloying (modification) of the surfaces with Zr, Nb, or Si and B. By analyzing the changes in the microhardness, structure, and thermoelectromotive force of the corresponding coatings on holding in the eutectic melt at 350 or 500°C for 10⁴ h, it is shown that the procedure of laser alloying may result in the formation of layers with long-term protective action.     

Columnar grain development in C-Mn-Ni low-alloy weld metals and the influence of nickel

This paper discusses the development of columnar grains in as-deposited C-Mn-Ni(-Mo) low-carbon low-alloy weld metals and the influence of the alloying elements, particularly nickel. It was found that the austenite columnar grain size prior to the - transformation of the weld metals was mainly controlled by the alloying contents rather than HAZ grains adjacent to the fusion boundaries, although the latter determined the size of the initial columnar grain size. The addition of nickel initially depressed the prior austenite grain size and subsequently dramatically coarsened it. This was related to the nickel equivalent (Ni_eq) of the weld metals and the peritectic reaction during the solidification process. Small columnar grains were associated with a Ni_eq between 3.4 and 6.2% which resulted in a peritectic reaction when the weld melt solidified, whilst a Ni_eq higher than 6.2% produced very large columnar grains because the weld pool would directly solidify into austenite and have a subsequent continuous growth.     

Laser surface alloying of 1045 AISI steel using Ni–CrB2 powder

Abstract

Laser surface alloying is a process whose purpose is to improve the surface properties by incorporating alloying elements into the surface. The advantages of using laser for surface treatment are: formation of a non-equilibrium or amorphous phase as well as homogenisation and refinement of the microstructure, all without affecting the substrate properties. Powder (50 wt-%Ni–50 wt-%CrB₂) was injected into a melt pool created by a CW–CO₂ laser on AISI1045 steel plates. In order to alloy the entire surface, the sample was scanned at scan speeds in the range of 600–6000 mm min^–1 and the laser power was in the range of 1750–2500 W. The powder feed rate was 1·6 g min^–1, the laser beam was 2 mm in diameter, with 60% overlap between successive laser paths. Metallographic cross-sections were made of the samples. For each sample the following properties were characterised: layer depth, microhardness (HV), layer microstructure and composition. It has been found that the scan speed and the laser power affect the depth of the melt pool, the microstructure, the hardness and the treated layer composition. The laser boronised surface exhibits better wear resistance than D2 tool steel hardened to 59 ± 1 HRC. This will be discussed based on numerical analysis of the laser/material interaction.     

Beschichten,Reparieren und Generieren durch Präzisions‐Auftragschweißen mit Laserstrahlen

Laser beam build‐up welding belongs to the technical group of thermal coating. With a coating thickness between 0.1 and 3 mm it is positioned close to PTA and TIG cladding. The special features consist in the excellent controllability of the cladding process, high precision of the material deposition, low thermal influence on the workpiece and low base material mixing, the absence of mechanical effects on the melt pool as well as the large number of coating and substrate materials available for the manufacturing process. Currently, the most important application is the repair of complex shaped and expensive components and tools. Examples are wear damaged moulds, metal forming dies, or aircraft engine components, which original properties can be completely restored by accurate and local replacement of the lost material. In the field of surface protection, laser technology offers advanced solutions for the surface modification of light alloys. Components of Ti, Al or Mg alloys can be protected effectively against wear and corrosion by laser cladding, alloying, and hard particle dispersing. Generating of metal Prototypes by CNC controlled Direct Metal Deposition is a further application of the laser technique. Using this method, mould inserts, active parts of tools, or engine components can be generated directly from the 3D CAD data.     

激光表面改性技术及其研究进展

激光表面改性技术是表面工程中的先进技术之一,其在先进制造与再制造领域的应用备受关注。本文概述了激光表面改性技术中的激光相变硬化、激光熔凝硬化、激光冲击硬化、激光合金化、激光熔覆等,介绍了以上几种激光表面改性技术的研究现状,最后对激光表面改性技术的发展与工程应用的前景进行了展望。     

Manufacturing and Microstructural Evolution of Mechanuically Alloyed Oxide Dispersion Strengthened Superalloys

Mechanical alloying is a process in which mixtures of powders are severely deformed until they form atomic solutions. Inert oxides can also be introduced to form a dispersion of fine particles which help strengthen the consolidated product. Significant quantities of iron and nickel‐base alloys, with unusual properties, are produced commercially using this process. The total true strain during mechanical alloying can be as large as 9; there is proof that this leads to mixing on an atomic scale and to the development of a uniform grain structure which is sub‐micrometer in size. Following mechanical alloying, the particles are consolidated using standard powder metallurgical techniques. The consolidated metal has a large stored energy, approaching 1 J g^–1. This ought to make it easy to induce recrystallisation, but in practice the alloys fail to recrystallise except at very high temperatures close to melting. On the other hand, the recrystallisation temperature can be reduced dramatically by slightly deforming the consolidated product prior to heat treatment. It is in this context that the solution formation, microstructure and mechanical properties of such alloys are reviewed here.     

Laser heat treatment of titanium GRADE 1 with iron‐nickel powder

Titanium alloys thanks to their low density and high mechanical properties are a group of materials that are being used willingly nowadays. A promising method of titanium heat treatment is laser alloying. Process parameters like laser beam power, its traverse speed, amount of alloying elements and shield gas, have influence on the resulting material. Different chemical composition and morphology can be achieved resulting in a change of properties on the surface of the material. The paper presents the investigation of titanium GRADE 1 processed with iron‐nickel powder using laser alloying. The treatment was performed using a high power diode laser. Different laser beam power values were used. Treatment resulted in obtaining good‐adhere, porous‐free, uniform composite material with no cracks. Formation of new phases and solid solution was the reason why it was possible to achieve an increase in microhardness on the surface. Light microscopy, scanning electron microscopy with energy dispersive X‐ray spectroscopy examination, microhardness results and X‐ray diffraction are presented within the paper.     

Effect of beam interaction time on laser alloying with pulsed Nd–YAG laser

Abstract

Surface alloying of aluminium with nickel was carried out using a pulsed Nd–YAG laser. The effect of beam interaction time on laser alloying of aluminium with pulsed Nd–YAG laser has been studied. It was found that the beam interaction time of a pulsed laser has a significant effect on microstructure and properties of alloyed layers. The results indicated that with changes in the beam diameter, higher thickness of alloyed layer and higher microhardness are both obtained at a lower effective interaction time. When travel speed changes, the same conditions are obtained at a higher effective interaction time.     

Using optical diagnostics to determine the melt temperature field in layer-by-layer laser alloying of metal powder

The results of application of optical diagnostics in the estimation of the temperature field at the melt surface in layer-by-layer laser alloying of metal powder are presented. It is demonstrated that surface concavity induced by the thermocapillary effect upon nonuniform heating may distort pyrometry data considerably. The use of external illumination provides an opportunity to determine the shape of the melt surface. The obtained minimum estimate of the temperature gradient in the metal region affected by laser radiation is 2.8 × 10⁴ K/cm.     

Molecular dynamics investigation of mechanical mixing in mechanical alloying

Molecular dynamic simulation is exploited to obtain a deep insight of atomic scale mixing and amorphization mechanisms happening during mechanical mixing. Impact–relaxation cycles are performed to simulate the mechanical alloying process. The results obtained by structural analysis shows that the final structure obtained through simulation of mechanical alloying is in an amorphous state. This analysis reveals that amorphization occurs concurrently with the attainment of a perfectly mixed alloy. The results indicate diffusion and deformation are two important mechanisms for mixing during mechanical alloying. The rate of diffusion is controlled by the temperature and by the density of defects in the structure. Deformation enhances mixing directly by sliding atomic layers on each other and increases the number of defects in the structure. The results agree with mechanical alloying experiments described in the literature.     

High-Entropy Alloy-Induced Metallic Glass Transformation: Challenges Posed by in situ Alloying via Additive Manufacturing

In situ alloying and fabricating glassy structures through a layer-by-layer fashion approach are challenging but have high potential to develop novel-graded materials. For the first time, this cost-effective approach is applied to additive manufacturing (AM) of a Zr-based bulk metallic glass (BMG) from high-entropy alloys (HEAs). A newly developed composition of Zr₄₀Al₂₀Cu₂₀Ti₂₀ is fabricated through laser powder bed fusion (LPBF). Process parameters are optimized within a wide range of laser power (50–200 W) as well as scanning speed (50–800 mm s⁻¹). In all printed samples, microscopic and compositional examinations reveal no glass formation, but very fine grains and CuTi and AlTi nanocrystals. Some glassy transitions at the interfaces may be encouraged to occur with proper melting and mixing. However, the main reason for not obtaining a glassy matrix is the substantial proportion of unmelted Zr raw powder throughout the structure as spherical particles. Consequently, glass formation can be hindered by a considerable amount of compositional deviation. During LPBF, in situ alloying poses significant challenges to developing BMGs. Hence, the various stages of the process, including raw material specifications, laser settings, and process parameters, should be investigated further.     

Suppression of moisture-induced embrittlement of Ni3(Si, Ti) alloys by a surface nickel alloying layer

The effect of a surface nickel alloying layer on moisture-induced embrittlement of Ni3(Si, Ti) alloys has been investigated by tensile tests at room temperature, using nickel-deposited materials. Undeposited Ni3(Si, Ti) alloy became remarkably embrittled in air. However, nickel-deposited Ni3(Si, Ti) alloy showed a high elongation value, indicating the suppression of embrittlement caused by hydrogen decomposed from moisture in the air. When the surface nickel alloying layer consists of f c c(γ) solid solution with a high nickel concentration and good adhesion to the substrate, improvement of tensile elongation is the greatest. The results have been discussed from the chemical and structural viewpoints of the surface nickel alloying layer. This revised version was published online in November 2006 with corrections to the Cover Date.