Microstructure Of Surface Layer Research Articles

Effects of Shot Peening and Cavitation Peening on Properties of Surface Layer of Metallic Materials-A Short Review.

Shot peening is a dynamically developing surface treatment used to improve the surface properties modified by tool, impact, microblasting, or shot action. This paper reviews the basic information regarding shot peening methods. The peening processes and effects of the shot peening and cavitation peening treatments on the surface layer properties of metallic components are analysed. Moreover, the effects of peening on the operational performance of metallic materials are summarized. Shot peening is generally applied to reduce the surface roughness, increase the hardness, and densify the surface layer microstructure, which leads to work hardening effects. In addition, the residual compressive stresses introduced into the material have a beneficial effect on the performance of the surface layer. Therefore, peening can be beneficial for metallic structures prone to fatigue, corrosion, and wear. Recently, cavitation peening has been increasingly developed. This review paper suggests that most research on cavitation peening omits the treatment of additively manufactured metallic materials. Furthermore, no published studies combine shot peening and cavitation peening in one hybrid process, which could synthesize the benefits of both peening processes. Moreover, there is a need to investigate the effects of peening, especially cavitation peening and hybrid peening, on the anti-wear and corrosion performance of additively manufactured metallic materials. Therefore, the literature gap leading to the scope of future work is also included.

A review on friction stir processing over other surface modification processing techniques of magnesium alloys

An enormous amount of research has been conducted on aluminium alloys in friction stir processing (FSP), despite magnesium alloys reporting severe weight reduction when compared to aluminium alloys; a very slight amount of research has testified for FSP of magnesium alloys. Magnesium is highly reactive and susceptible to corrosion in the presence of an aggressive environment. This highly corrosive nature of magnesium limits its applications. Surface properties like crystal structure, composition, and microstructure influence the corrosion and wear properties of the material. Coating techniques and alloying techniques like laser surface modifications are performed to passivate the magnesium surface from corrosion. Coating techniques, however, have been found to be insufficient in corrosion protection due to coating defects like pores, cracks, etc, adhesion problems due to poor surface preparation of the substrate, and impurities present in the coating which provide microgalvanic cells for corrosion. The current study gives a detailed overview of different types of surface modification methods, such as physical vapour deposition, chemical vapour deposition, chemical conversion coating, and ion implantation coating techniques, and also focuses on a few alloying or surface processing methods, such as laser surface modification – namely laser surface melting, laser surface cladding, laser shot peening, laser surface alloying and FSP. FSP is a novel surface modification method derived from friction stir welding, which modifies the microstructure and composition of surface layer without changing the bulk properties to enhance corrosion resistance. FSP enhances and homogenizes the microstructure but also eliminates the breakup of the brittle-network phases and cast microstructure imperfections. Indeed, FSP can produce particle and fibre-reinforced magnesium-based surface composites. FSP empowers the manufacturing of magnesium by adding additives. The different methods of coating and surface modification are compared with FSP.

Surface globularization generated by standard PBF-EB Ti-6Al-4V processing achieves an improvement in fatigue performance

Standard electron beam powder-bed fusion Ti-6Al-4V powder recovery and hot-isostatic pressing has been found to result in a surface layer microstructure change to globular α/β. Thickness control of this surface layer up to 15μm was demonstrated by varying powder recovery blasting working distance and duration. This surface globular layer was found to improve high-cycle rotating bending fatigue strength at 107 cycles by 60 MPa for specimens with smooth surfaces. The same trend was not observed for specimens with as-built surface roughness because globularization did not occur at dominant fatigue crack initiation sites; the roots of deep surface crevices.

Effect of Nano-Y2O3 on the Microstructure and Properties of WC-Reinforced Ni-Based Composite Surfacing Layer.

In this study, a WC-reinforced Ni-based surfacing layer was prepared on Q235 steel plate by plasma arc welding. The effects of nano-Y2O3 with different contents (0 wt.%, 0.4 wt.%, 0.8 wt.%, 1.2 wt.%, and 1.6 wt.%) on the microstructure, phase composition, microhardness, and wear resistance of the surfacing layer were studied by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), microhardness test, and pin-on-disk test. The results show that the phase composition of the surfacing layer was γ-Ni, FeNi3 solid solution, WC, W2C, M23C6, M6C, Cr7C3, and other carbides. When the addition of nano-Y2O3 was 1.2 wt.%, it has a good improvement on microstructure grain refinement and carbide hard-phase increase. Compared with other contents, 1.2 wt.% nano-Y2O3 surfacing layer has the highest microhardness and the lowest friction coefficient and wear loss. At this time, the wear mechanism is abrasive wear accompanied by slight adhesive wear.

Microstructure and high-temperature oxidation behaviors of surface layer on TA2 pure titanium by boriding and aluminizing two-steps method

The surface layer on pure TA2 titanium was manufactured using boriding and aluminizing two-step methods. High-temperature oxidation experiments were carried out at 600 °C, 700 °C, and 800 °C for 100 h. Microstructure characterization of the surface layer was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). After 1050°C-4 h boriding and 1050°C-4 h aluminizing, the composite layer from the surface to the matrix consists of a TiB2 layer, TiB whisker + Al3Ti layer, Al3Ti layer, and diffusion layer. The Al3Ti layer could effectively protect the matrix, and thus, the borided and aluminized pure titanium shows excellent high-temperature oxidation resistance.

Effect of ultrasonic forging strain processing on the surface layer microstructure and temperature-dependent mechanical properties of high nitrogen austenitic steel

The paper presents the research results on the effect of ultrasonic forging strain (UFS) processing of the high-nitrogen Cr–Mn–N austenitic stainless steel on the surface layer microstructure and tensile properties in the temperature range from −80 up to 20 °C. The high dispersion microstructure, strain aging with the formation of both CrN and Fe2N nitrides, as well as twinning were revealed in the surface layer 2–3 μm thick using a transmission electron microscope (TEM). In addition, ε-martensite with the hcp lattice was observed at a depth of more than 80 μm from the surface after UFS processing. Tensile tests showed that UFS processing had increased the yield strength. Elongation level of about 40% did not differ over the entire test temperature range. A ductile type of the fracture surfaces was observed for all test temperatures down to −80 °C.

Laser Processing of Diffusion Boronized Layer Produced on Monel® Alloy 400-Microstructure, Microhardness, Corrosion and Wear Resistance Tests.

The paper presents the results of studies of microstructure, mechanical and physicochemical properties of surface layers produced by laser modification of the diffusion boron layer on Monel® Alloy 400. The diffusion boron layers were produced at 950 °C for 6 h. The gas-contact method was used in an open retort furnace. The process was carried out in a powder mixture containing B4C carbide as a boron source. The next stage was the modification of the boron layer with a diode laser beam of a nominal power of 3 kW. A constant power of 1400 W of the laser beam was used. The scanning speed was variable (successively 5 m/min, 25 m/min, 50 m/min). In order to determine the best parameters, single tracks were created, after which multiple tracks were prepared using previously selected parameters. It was found that both the diffusion borided layer and the laser modified layer had better properties than the substrate material. Both these processes contributed to an increase in corrosion resistance, hardness and wear resistance. It was also found that laser modification caused a slight deterioration of the properties in comparison with the diffusion borided layer. However, the laser modification process resulted in the production of a much thicker layer.

Indentation behavior of creep-feed grinding induced gradient microstructures in single crystal nickel-based superalloy

The gradient microstructures of surface layer in single crystal nickel-based superalloy were produced by creep-feed grinding. The mechanical properties (i.e., hardness, elastic modulus) and room-temperature (RT) creep behavior of such structures were evaluated using a nano-indentation technique. Results show that the gradient structures along depth from ground surface consisted of nanograins, submicron grains and lamellar-shape structures, and dislocation structures. Furthermore, it was found that the hardness and elastic modulus of gradient structures were higher by 8–10% than that of bulk material on average. However, the regions containing nanograins showed a remarkable increase in creep depth compared to bulk material, implying that the creep behavior of ground layer was changed unfavorably. The obtained stress exponents of gradient structures suggested that dislocation activities were the main mechanism for indentation creep deformation.

High-Temperature Oxidation Behavior of AlTiNiCuCox High-Entropy Alloys.

In this study, the high-temperature oxidation behavior of a series of AlTiNiCuCox high-entropy alloys (HEAs) was explored. The AlTiNiCuCox (x = 0.5, 0.75, 1.0, 1.25, 1.5) series HEAs were prepared using a vacuum induction melting furnace, in which three kinds of AlTiNiCuCox (x = 0.5, 1.0, 1.5) alloys with different Co contents were oxidized at 800 °C for 100 h, and their oxidation kinetic curves were determined. The microstructure, morphology, structure, and phase composition of the oxide film surface and cross-sectional layers of AlTiNiCuCox series HEAs were analyzed using scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and X-ray diffraction (XRD). The influence of Co content on the high-temperature oxidation resistance of the HEAs was discussed, and the oxidation mechanism was summarized. The results indicate that, at 800 °C, the AlTiNiCuCox (x = 0.5, 1.0, 1.5) series HEAs had dense oxide films and certain high-temperature oxidation resistance. With increasing Co content, the high-temperature oxidation resistance of the alloys also increased. With increasing time at high temperature, there was a significant increase in the contents of oxide species and Ti on the oxide film surface. In the process of high-temperature oxidation of AlTiNiCuCox series HEAs, the interfacial reaction, in which metal elements and oxygen in the alloy form ions through direct contact reaction, initially dominated, then the diffusion process gradually became the dominant oxidation factor as ions diffused and were transported in the oxide film.

Prevention in Thermal Crack Formation in Chabazite (CHA) Zeolite Membrane by Developing Thin Top Zeolite and Thick Intermediate Layers.

Chabazite (CHA) zeolite membranes with an intermediate layer of various thicknesses were prepared using planetary-milled seeds with an average particle diameter of 300, 250, 200, 140, and 120 nm. The 120 nm seed sample also contained several smaller particles with a diameter of 20 nm. Such small seeds deeply penetrated into the pore channels of the α-alumina support during the vacuum-assisted infiltration process. During the secondary growth, the penetrated seeds formed a thick intermediate layer exiting between the zeolite layer and support. A decrease in seed size increased the penetration depth of seeds and the thickness of the intermediate layer, while the thickness of seed coating and zeolite layers was decreased. CHA zeolite membranes with a thin top zeoliate layer and a thick intermediate layer showed an excellent water/ethanol separation factor (>10,000) for 90 wt.% ethanol at 70 ℃ with a total flux of 1.5 kg m−2 h−1. There was no observation of thermal cracks/defects on the zeolite separation layer. The thick intermediate layer effectively suppressed the formation of thermal cracks during heating, since the tensile stress induced in the zeolite layer was well compensated by the compressive stress on the support. Therefore, it was successfully proven that controlling the microstructure of top surface and intermediate layers is an effective approach to improve the thermal stability of the CHA zeolite membrane.

Distributions of grains and precipitates in gradient lamellae Al–Zn–Mg–Cu alloy by ultrasonic surface rolling processing

Improving surface properties can effectively expand the industrial application of aluminum alloys. In this study, a gradient nanostructured surface layer was successfully fabricated in an aged Al–Zn–Mg–Cu alloy by ultrasonic surface rolling processing (USRP). The microstructure and microhardness of the gradient nanostructured surface layer were investigated. The results show that a perfect gradient lamellae structure was fabricated in the surface layer. The average structural size in the topmost surface layer is approximately 41 nm, and the depth of nanostructure lamellae layer is up to 50 μm. After the USRP and two years of natural aging, the gradient distribution of precipitates was formed in gradient lamellae structure. A large number of discontinuous coarse η phase are formed on the lamellae boundary throughout the lamellae structure. However, the precipitates inside the lamellae have gradient distribution. The volume fractions of precipitates increase gradually from nanostructure to ultrafine-grained structure, and the main precipitates are GPII zones. The microhardness in the topmost surface is increased by 40% and gradually decreases from the surface to the matrix. The increase in microhardness is attributed to the fact that the enhancement of the hardness by the grain refinement is greater than the decrease due to the reduction of the precipitates inside the gradient lamellae structure from the surface to the matrix. This study provides technical method and theoretical basis for improving the surface hardness of Al–Zn–Mg–Cu alloy.

Microstructural evolution and surface integrity of ultrasonic surface rolling in Ti6Al4V alloy

Ultrasonic surface rolling technology is a new mechanical surface treatment technology that can improve the surface integrity, increase the amplitude and depth of the residual compressive stress layer and improve the fatigue property of metal materials. In this paper, the effect of ultrasonic rolling on the surface layer's microstructure and properties of Ti6Al4V alloys is investigated. The microstructure, surface roughness, surface topography, microhardness and residual stress were used to characterise the surface-modified layer. Specimens treated by ultrasonic surface rolling obtained the smallest surface roughness (0.231 μm) and largest plastic deformation depth (304.38 μm), simultaneously, under sixteen processing stage numbers. The rule of surface compressive residual stress distribution had a similar tendency to the law of surface microhardness distribution. Furthermore, the grain size of the strengthened surface layer decreased, the texture type changed and the Schmidt factor increased compared with the matrix. The increase of microhardness and residual stress is due to grain refinement and dislocation strengthening.

Microstructure and Abrasive Wear Resistance of Metal Matrix Composite Coatings Deposited on Steel Grade AISI 4715 by Powder Plasma Transferred Arc Welding Part 2. Mechanical and Structural Properties of a Nickel-Based Alloy Surface Layer Reinforced with Particles of Tungsten Carbide and Synthetic Metal-Diamond Composite.

The article is the continuation of a cycle of works published in a Special Issue of MDPI entitled “Innovative Technologies and Materials for the Production of Mechanical, Thermal and Corrosion Wear-Resistant Surface Layers and Coatings” related to tests concerning the microstructure and mechanical properties of innovative surface layers made using the Powder Plasma Transferred Arc Welding (PPTAW) method and intended for work surfaces of drilling tools and machinery applied in the extraction industry. A layer subjected to tests was a metal matrix composite, made using powder based on a nickel alloy containing spherical fused tungsten carbide (SFTC) particles, which are fused tungsten carbide (FTC) particles and spherical particles of tungsten-coated synthetic metal–diamond composite (PD-W). The layer was deposited on the substrate of low-alloy structural steel grade AISI 4715. The results showed that the chemical composition of the metallic powder as well as the content of the hard phase constituting the matrix enabled the making of a powder filler material characterised by very good weldability and appropriate melting. It was also found that the structure of the Ni-WC-PD-W layer was complex and that proper claddings (characterised by the uniform distribution of tungsten carbide (WC)) were formed in relation to specific cladding process parameters. In addition, the structure of the composite layer revealed the partial thermal and structural decomposition of tungsten carbide, while the particles of the synthetic metal–diamond composite remained coherent. The deposited surface layer was characterised by favourable resistance to moderate dynamic impact loads with a potential energy of 200 J, yet at the same time, by over 12 times lower metal–mineral abrasive wear resistance than the previously tested surface layer made of cobalt-based composite powder, the matrix of which contained the hard phase composed of TiC particles and synthetic metal–diamond composite. The lower abrasive wear resistance could result from a different mechanism responsible for the hardening of the spherical particles of the hard phase susceptible to separation from the metal matrix, as well as from a different mechanism of tribological wear.

Mechanical Properties of Nitrided Layer after Laser Modification

The aim of this work was to study the microstructure and friction coefficient of hybrid surface layers, produced by a controlled gas nitriding and laser modification. Nitriding is well-known technique of thermo-chemical treatment, applied in order to produce the surface layers of improved hardness and wear resistance. The phase composition and growth kinetics of the diffusion layer can be controlled using a gas nitriding with changeable nitriding potential. 42CrMo4 steel was treated by composite technology of gas nitriding and laser hardening. The nitriding processes were carried out at temperature of 580 °C for 8h. Next, the nitrided layer was laser-modified using laser TRUMPF TruDiode 3006 with maximal power of 3 kW using the two laser beam powers (P): 0.53 kW and 0.62 kW. Then, the microstructure and properties of the laser-modified nitrided layers were investigated using optical microscopy, Vickers hardness tester and friction wear testing machine. The nitrided layers were subjected to wear tests using a ball-on-disc method at room temperature. The results showed that the microstructure of the produced hybrid layers consisted of the re-melted and heat-affected zones in which martensite mainly occurred. Additional laser treatment effectively increased the hardness, especially in heat-affected zone, as well as the depth of the hardened layer. The layer after modification laser hest tretment were good friction coefficien. The curve of the friction coefficient after the nitrided layer was characterized by large fluctuations. Compared with nitriding technology , the hybrid treatment technology can effectively increase the hardness and wear resistance of the 42CrMo4 steel surface. The effect of LHT on the tribological properties was ambiguous. Although the relatively low value of the average friction coefficient (0.46) was calculated for nitrided layer, the course of friction coefficient was characterized by large fluctuations and the extended grinding-in time. Simultaneously, the course of friction coefficient was very smooth after nitriding and LHT. However, the average friction coefficient were higher, obtaining 0.60 and 0.57 for the hybrid layers, produced using P=530 W and P=620 W, respectively. Keywords: Nitriding; Laser Heat Treatment; Microstructure; Wear Resistance; Microhardness

Novel micron-thick brick cladding of polyfluorosilicone acrylates, a case study of conservation of historic brick wall in Hongcun village

A micron-thick (3–5 μm) and transparent cladding technique based on the environment friendly dimethyl carbonate solution of newly developed polyfluorosilicone acrylates was successfully applied to restore the surface of brick walls of a historic house which has been severely eroded by damp and mildew for more than 300 years in Hongcun village, one of the World Heritage sites in China. The restoration followed the rule of repairing old as old before. The cladding made from the copolymerized polyfluorosilicone acrylate resin, which mainly contained the chain fragments of dodecafluoroheptyl methacrylate and 3-(trimethoxysilyl)propyl methacrylate, permeated through the surface of old brick with an average depth of 14.5 mm in this case study, and provided an ultrathin and efficient covering of the microstructure of the shallow surface layer of old bricks and resulted excellent water-proof, moisture-proof, mildew-proof and long-lasting weather resistance effects. The water contact angle of the treated surface of the old bricks reached 133°, the water absorption of treated bricks was reduced from 16.1 wt% to 2.8 wt% after soaking in water for 24 h.

Surface Treatment of Cementitious Composites by Ultrasound and Its Effect on Durability Performance

AbstractIn this study, the method of changing the surface layer microstructure of cementitious composites by ultrasonic surface treatment at the early stage of hydration is introduced, and the form...

The effect of varying porosity and inhomogeneities of the surface dust layer on the modelling of comet gas production

ABSTRACT We study how uncertainties in knowledge of the microstructure of the porous dust surface layer affect our estimates of effective gas production of comet 67P/Churyumov-Gerasimenko. We analyse the transport properties (distribution of free paths, mean pore size, permeability) for random densely packed porous layers. Bimodal layers, as well as various cases of inhomogeneous layers having cavities and cracks, are considered. Modelling is performed for various values of effective porosity and various particle sizes and thicknesses of the dust layer. The results of computer simulations are embedded in thermal models of the surface region of the cometary nucleus, including explicitly a radiation thermal conductivity and a resistance of the dust layer for the gas flow is used. The simulations show that the porosity variations within the range of values expected for the 67P can change the effective gas production by tens of percent for thin layers, and can vary by several times with increasing layer thickness. These effects are manifested at all heliocentric distances where sublimation of water ice makes a significant contribution to the energy budget of the nucleus. Modelling also shows that in all considered cases the microscopic cavities and cracks have a minor effect on the effective gas production: changes in the presence and number of inhomogeneities in comparison with a uniform layer of the same effective porosity are negligible.

Microstructure and phase composition of surface layers formed on aluminium alloys by plasma electrolytic oxidation

This paper presents elaboration and structural characterization of surface layers formed on aluminumalloys by plasma electrolytic oxidation (PEO). The electrolyte is a mixture consisting: sodium metasilicate and sodium hydroxide. The coatings obtained by PEO were investigated with: scanning electron microscopy (SEM) with Energy dispersive X-ray spectrometer (EDX) and X-ray diffraction (XRD)techniques.

Structuring of the Ti6Al4V alloy surface by pulsed laser remelting

In this work, we present experimental data on the structure, chemical composition and wear resistance of a titanium alloy Ti6Al4V after pulsed laser treatment. The material was investigated to get a better understanding of the nature of laser melting, ablation of the surface layer by using nanosecond, picosecond, and femtosecond lasers. Melting and subsequent rapid solidification forms a new changed microstructure of the Ti6Al4V surface layer. This rapid solidification of the surface layer affects the new microstructure as well as its surface’s topography (texture). It is shown that using different laser’s pulse parameters the desired surface topography (texture) of the Ti6Al4V can be obtained.The laser treatment with femtosecond and picosecond pulse allows creating periodical micro/nano structures on the surface. These structure are characterized by good wear resistance as compared with the non-texturized surface of Ti6Al4V. In the case of nanosecond laser surface treatment of the Ti6Al4V elements, it is possible to obtain the strongly extended surface of Ti6Al4V elements in the form of metal-oxide foam that is also characterized with good wear resistance. The laser treatment with femtosecond and picosecond pulse allows creating periodical micro/nano structures on the surface. These structure are characterized by good wear resistance. In the case of nanosecond laser surface treatment of the Ti6Al4V elements, it is possible to obtain the strongly extended surface of Ti6Al4V elements in the form of metal-oxide foam. Analysis of the foam microstructure shows that the α-Ti phase was transformed mostly into β-Ti, and is significantly fragmented.

Microstructure and property modifications in surface layers of a Mg-4Sm-2Al-0.5Mn alloy induced by pulsed electron beam treatments

In this work, surface modification of a Mg-4Sm-2Al-0.5Mn alloy with high current pulse electron beam (HCPEB) under different number of pulses were investigated. The evolution in microstructure, composition and phase components and properties in the surface layer before and after HCPEB treatment were characterized. It was found that the Al 11 Sm 3 and Al 2 Sm phases in the surface layer were gradually dissolved during HCPEB treatment, leading to the formation of a chemical homogeneous melted layers. Besides, deformation bands were formed in the treated layer due to the thermal stress generated during treatment. After 15 pulses treatment, the surface hardness increases to the maximum value of about 62.2 HV, about 61.2% higher than that of the untreated state. Electrochemical results show that the 15 pulses treated sample presents the best corrosion resistance in the 3.5wt% NaCl water solution by showing the highest corrosion potential ( E corr ) of -1.339V SEC and the lowest corrosion current density ( I corr ) of 1.48 × 10 −6 A·cm −2 . The results prove that the surface properties of the Mg-4Sm-2Al-0.5Mn alloy can be significantly improved by the HCPEB treatments under proper conditions.