Microstructure Of Surface Layer Research Articles

Formation of Nano-Sized Structural-Phase States in Surface Layers of a Cermet Alloy and the Influence of the States on the Tool Life of Cermet Plates in Metal Cutting

A comparative analysis of the surface-layer microstructure of a tungsten-based cermet alloy modified with pulsed high-energy electron beams generated by gas-discharge plasmas and of the tool life of metal-cutting plates prepared from this alloy is performed. The choice of a plasma-forming gas providing for the emission of electrons out of the plasma-filled cathode is shown to have a profound influence both on the formation process of nanosized structural-phase states in the surface layer of the cermet alloy and on the tool life of the metal-cutting plates prepared from this alloy.

Effects of injection molding conditions on the electrical properties of polycarbonate/carbon nanotube nanocomposites

Polycarbonate/Carbon nanotube (PC/CNT) nanocomposites containing various CNT contents (0–5 wt%) were prepared by injection molding. The effects of CNT contents, injection speed (V) and injection temperature (T) on the electrical resistivity of the PC/CNT nanocomposites were investigated. It was found that the tensile strength of nanocomposites was enhanced slightly with increased CNT contents, and the tensile modulus was 29% greater after the 5 wt% CNT addition, but the brittle tendency became stronger. Aside from tensile properties, the electrical resistivity of the nanocomposites dropped 12 orders of magnitude after the 5 wt% CNT addition. Also, there was a tendency that the electrical resistivity was lower in the case of higher injection temperature and lower injection speed. Scanning electron microscope (SEM) images and the distribution of surface layer electrical resistivity, clearly showed a notable influence by surface layer microstructures on the electrical resistivity, and the injection conditions affected both the value of the maximum electrical resistivity and the position where it occurred. This study offers an alternative green and simple molding process to prepare conductive PC nanocomposites and to achieve the industrialization of PC/CNT nanocomposite products which can be used in electromagnetic shielding and anti‐static fields. POLYM. COMPOS., 37:3245–3255, 2016. © 2015 Society of Plastics Engineers

Effect of low doses beta irradiation on micromechanical properties of surface layer of injection molded polypropylene composite

Abstract The influence of beta radiation on the changes in the structure and selected properties (mechanical and thermal) was proved. Using low doses of beta radiation for 25% glass fiber filled polypropylene and its influence on the changes of micromechanical properties of surface layer has not been studied in detail so far. The specimens of 25% glass fiber filled PP were made by injection molding technology and irradiated by low doses of beta radiation (0, 15 and 33 kGy). The changes in the microstructure and micromechanical properties of surface layer were evaluated using FTIR, SEM, WAXS and instrumented microhardness test. The results of the measurements showed considerable increase in micromechanical properties (indentation hardness, indentation elastic modulus) when low doses of beta radiation are used.

Mechanical properties and thermal stability of nanocrystallized pure aluminum produced by surface mechanical attrition treatment

By means of surface mechanical attrition treatment (SMAT), nanocrystalline surface layers were generated in pure aluminum (Al) sheet. The microstructure of the nanocrystalline surface layer was systematically characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that dislocation slip is the main mechanism for grain refinement of Al with SMAT. The mechanical properties were tested by uniaxial tensile and micro-hardness tests. After SMAT, the yield strength of the nanostructured Al was about two times higher than that of the coarse-grained counterpart, with compromise of elongation. The relationship between microstructure and mechanical properties of Al with SMAT was discussed. Moreover, the Al sample after SMAT exhibits a much faster strain hardening rate reduction and a weaker strain hardening than the one without SMAT. Furthermore, the thermal stability of the nanocrystalline surface layer was studied by isothermal and isochronal annealing treatments at the temperature range from 155°C to 355°C. It reveals that such nanocrystalline surface layer of Al exhibits high thermal stability, which can be retained up to 275°C. The growth kinetics of nano-sized grain of Al subjected to SMAT was investigated.

Microstructure of surface layer of T1 and D2 steels after laser melting

The aim of this study was to investigate the in-depth structure transformations of the laser-melted layers of the steels mostly used in tool production – T1 and D2 steels. The experiments of laser surface melting of T1 and D2 steels were done with continuous wave CO2 laser (wavelength λ = 10.6 μm). The sample’s microstructure was investigated, and the EDX analysis was made by SEM JEOL JMS-35C. Our results show that the microstructural changes of the laser-melted layer of T1 steel were determined by the process of directed crystallisation from the bottom layer to the surface. There is considerable inhomogeneity, followed by the predominantly ongoing process of chemical liquation during crystallisation. Cellular structure, consisting high-carbon martensite and significant amount of retained austenite, prevails in the melted pool bottom. Austenite–carbide eutectic with possible presence of lamellar martensite is situated along the dendrites’ boundaries (in inter-dendrite spaces). The austenite–carbide quasieutecticum with carbide-type M6C possesses ‘skeletal’ morphology in these regions. In the laser melting of D2 steel, the phase transformations in the transition zone (liquid–solid state) were defined by running of reverse eutectic reaction at the places of overheated and partially melted carbide phases. During cooling of these regions, the inhomogeneous melt goes through changes that involve precipitation of oversaturated with carbon and chrome austenite and disperse microquasieutectic with carbides of the M7C3 type.

Effect of high energy shot peening pressure on the stress corrosion cracking of the weld joint of 304 austenitic stainless steel

The weld joint of 304 stainless steel is treated using high energy shot peening(HESP) with various shot peening pressures. The grain size and metallographic microstructure of the specimen surface layer are analyzed using the X-ray diffraction method, and the surface hardness is measured. Slow strain rate tension tests are then performed to investigate the effect of shot peening pressure on the stress corrosion sensitivity. The results show that in the surface layer of the specimen, the grain refinement, hardness and the strain-induced plastic deformation all increase with the increasing shot peening pressure. Martensitic transformation is observed in the surface layer after being treated with HESP. The martensite phase ratio is found to increase with increasing shot peening pressure. The result also shows that the effects of the shot peening treatment on the stress corrosion sensitivity index depend on the shot peening pressure. When the shot peening pressure is less than 0.4MPa, the grain refinement effect plays the main role, and the stress corrosion sensitivity index decreases with the increasing shot peening pressure. In contrast, when the shot peening pressure is higher than 0.4MPa, the martensite transformation effect plays the main role, the stress corrosion sensitivity index increases with increasing shot peening pressure.

Producing nanostructured Co–Cr–W alloy surface layer by laser cladding and friction stir processing

Abstract

Microstructure and Wear Resistance of Surface Layer of Copper Modified by N+ Ion High Fluencies Implantation

Change of the wear resistance of a copper couple under friction during nitrogen ion implantation was investigated using tribological tests in argon atmosphere. The structural-phase state of the treated sample surface was investigated by TEM, the microhardness was determined using nanoindenter, the penetration depth of nitrogen ions was investigated by the secondary ion mass spectrometry. It was established that the high nitrogen fluencies under ion implantation increase wear resistance of a copper friction pair 1.5-4.5 times as well as the microhardness of the sample surface.

ЛАЗЕРНАЯ ТЕРМИЧЕСКАЯ ОБРАБОТКА КОЛЬЦЕВЫХ ВЫСТУПОВ ИЗ ПОРОШКОВОЙ МЕДИСТОЙ СТАЛИ (ПСЕВДОСПЛАВА СТАЛЬ–МЕДЬ)

There were described results of investigations of microstructure and micro hardness of surface layer of collar step on disk plate from powder pseudo alloy steel – copper after carrying out of laser thermal treatment by fiber laser with capacity of 1 kW. There was revealed that under laser thermal treatment of pseudo alloy steel – copper except of full melting zone is developed field of partial flashing, that occurred in the volumes of low-melting component (cop- per) in parent structure and contacting sites of steel matrix. Then followed zone of quenching from solid state, in which for better samples was reached maximum micro hardness up 1000 HV in the volume of martensite, forming in perlite colony of initial material steel – copper.

An Analytical Investigation on the Effects of Heat Input on Microstructures, Phase Transformations and Mechanical Properties of Ultrafine Grained Mg Alloys Fabricated by Friction Stir Processing in Different Velocity Ratios

Friction stir processing is a solid state technique for partial modification of microstructures in surface layers of metals. Heat input is one of the efficient factors in this process which can vary the mechanical properties and the grains size even up to nano scale. In the present study, the effects of different rotational to traverse velocity ratio and also the circumstances of each one's effects on heat input were investigated during FSP of Mg alloys. Microstructure analyses were implemented in order to gain some concepts of heat input effects on the structures of the stirred zone. In the next step, the microhardness measurements were also calculated by a hall-petch type equation according to the grains size of the microstructures. The results indicate that increase in heat input leads to increase in grain size and decrease in hardness in the process zone. This phenomenon occurs because of complex interactions between dynamic recrystallization and grain growth during increasing heat input. The results also showed that there is always an optimum velocity ratio which disorder the balance, thereby maximizes the dynamic recrystallization and minimizes the grain growth in order to gain the minimum possible grain size in this process.

Microstructure and Properties of Surface Layer of Carburized 38CrAlMo6-10 Steel Subjected to Nanostructurization by a Heat Treatment Process/ Struktura I Właściwości Warstwy Naweglanej Na Stali 38Cralmo6-10 Po Procesie Nanostrukturyzacji W Warunkach Obróbki Cieplnej

Abstract The aim of the study was to produce and characterize a nanobainitic microstructure in surface layers of carburized 38CrAlMo6-10 structural steel. Steel contained 1.% Al and 0.3% Si - elements hindering the cementite precipitation, which was considered to be adequate for obtaining a carbide free bainite. Steel samples were subjected to two different vacuum carburizing processes in order to obtain two different contents of carbon in surface layer. To produce a nanobainitic microstructure a heat treatment consisting of austempering at temperature slightly higher than the martensite start temperature (Ms) of the layer was applied after each carburization process. It was found, that the obtained microstructure of carburized layer depends strongly on carbon content. In steel with surface layer containing lower carbon content a nanobainitic microstructure with carbon-enriched residual austenite was formed. In case of surface layer containing higher carbon content the ultra-fine grained lower bainite was obtained.

Phase Structure, Wear Resistance and Antimicrobial Response of Austenitic Stainless Steels 316L by Sputtering Cu during Plasma Nitriding and PECVD of Silicon Nitride

The surface of stainless steel 316L was plasma nitrided and subsequently deposited with silicon nitride from tetraethylorthosilicate (TEOS):H2:N2 gas mixtures by plasma enhanced chemical vapor deposition (PECVD). A copper mesh was employed to sputter copper atoms onto the surface during the two processes to consider its effect on the microstructure, tribology and antibacterial response of hard surface layers. The surface layers were characterized using XRD, optical and SEM microscopy, EDX analysis, microhardness test, pin-on-disc wear tests and microbial viability test. α-Si3N4 was found on the top surfaces of two steps processed stainless steel 316 L. Fe2–3N, Fe4N and CrN were identified in the compound layers. The overall thickness of the surface layers were more than 60 µm. The two step treatments improved the hardness up to 1600 HV0.1. The combination of plasma nitriding (with Cu sputtering) and PECVD of silicon nitride compound (with Cu sputtering) of SS 316 L resulted in superior high hardness, 3 times lower friction and 10 times higher wear resistance of treated surfaces if compared to those of conventional plasma nitrided surfaces. Cu addition to single plasma nitriding resulted in an effective reduction of 100% of Escherichia coli (E. coli) within 2 to 3 h. However the bacteria viability after the two step processes with Cu addition diminished to zero in 3.5 to 4 h. The antimicrobial response of the surfaces depends mainly on the Cu action and does not interfere with the wear resistance of the surfaces.

Friction, wear and plastic deformation of Cu and α/β brass under lubrication conditions

Friction, wear and plastic deformation of copper (Cu) and α/β brass were studied under lubrication conditions. Hardness and microstructure of surface layers were evaluated. The friction properties were presented by Stribeck curves. The friction coefficient and wear of brass were significantly larger in comparison to Cu. The critical load of transition from the elasto-hydrodynamic lubrication (EHL) to boundary lubrication (BL) was two times lower for brass. Superplastic deformation of α-phase grains in brass is appeared under friction in BL, whereas plastic deformation localized at thin surface layers is observed for Cu. Intragranular sliding in α-phase is accompanied with the formation of shear bands and many pores coalesced to cracks. Thickness of the wear particles of brass is close to the width of shear bands. The deformation hardness of brass is significantly higher in comparison to Cu rubbed in the BL region.

Nitriding of surface Mo-enriched sintered iron: Structure and morphology of compound layer

The trend in modern materials science is the development of composite materials and coatings with a combination of mechanical properties that provide higher strength and reliability of machine parts and tools. The deposition of composite coatings can be performed using plasma technology, such as enrichment of the metal surface with alloying elements and subsequent nitriding.In this work a pulse glow discharge was used to enrich a superficial layer with molybdenum (Mo) and then the nitriding treatment was conducted at high nitrogen concentration for the development of a compound layer. The present study involves an analysis of a compound layer formed on powder metallurgy (PM) parts, sintered with simultaneous surface enrichment and then, nitrided. Both the treatments were assisted by plasma technology. In particular, whether the alloying element Mo is incorporated (dissolved) into the iron nitrides that were formed was investigated. The different microstructures of the Mo-enriched surface layer in sintered iron after plasma nitriding have been investigated by employing light; scanning and transmission electron microscopy (SEM and TEM); X-ray diffraction (XRD); and hardness measurements. Analysis of the entire enriched layer and of the surface of samples demonstrated that Mo is present in the surface as γ-Mo2N fine precipitates and is incorporated into the iron nitrides in the compound layer.

Structure and properties of nitrided surface layer produced on NiTi shape memory alloy by low temperature plasma nitriding

NiTi shape memory alloys are used for bone and cardiological implants. However, on account of the metallosis effect, i.e. the release of the alloy elements into surrounding tissues, they are subjected to various surface treatment processes in order to improve their corrosion resistance and biocompatibility without influencing the required shape memory properties.In this paper, the microstructure, topography and morphology of TiN surface layer on NiTi alloy, and corrosion resistance, both before and after nitriding in low-temperature plasma at 290°C, are presented. Examinations with the use of the potentiodynamic and electrochemical impedance spectroscopy methods were carried out and show an increase of corrosion resistance in Ringer's solution after glow-discharge nitriding. This surface titanium nitride layer also improved the adhesion of platelets and the proliferation of osteoblasts, which was investigated in in vitro experiments with human cells. Experimental data revealed that nitriding NiTi shape memory alloy under low-temperature plasma improves its properties for bone implant applications.

NEW PECULIARITIES OF FRICTION SURFACE STRUCTURE OF BABBITT

Microstructure and properties of friction surface layers of the babbitt cover after boundary friction regime are studied by the optical, SEM and AES methods. New peculiarities of a structure of surface sub-micro-grains are found

Effects of laser shock peening and groove spacing on the wear behavior of non-smooth surface fabricated by laser surface texturing

Abstract The friction coefficient and wear resistance of non-smooth surface with different conditions are studied in this work. First, the effects of groove spacing on the friction behavior and wear resistance of the non-smooth surface are investigated. Second, the effects of massive laser shock peening (LSP) impact on the dry sliding wear performance of the non-smooth surface manufactured by laser surface texture (LST) are evaluated. In addition, the worn surfaces and typical microstructure in the top surface layer of all samples were characterized by field emission scanning electron microscope (SEM) with an EDS elemental analysis and transmission electron microscopy (TEM). The influence process of groove spacing and LSP on the friction behavior and wear resistance of T9 tool steel are also analyzed and discussed.

Influence of severe shot peening on wear behaviour of an aluminium alloy

ABSTRACTRecent developments in shot peening demonstrate that it can be applied using unconventional parameters in order to obtain nanocrystals on a thin surface layer of the treated material. These microstructural modifications have shown to be able to induce superior fatigue and corrosion properties, but still few data are available about their effect on wear behaviour of the materials.In this study, four series of Al 6063 alloy specimens, as‐received, conventionally shot peened, severely shot peened and severely shot peened followed by a slight mechanical grinding are subjected to block on ring wear tests with lubrication, according to ASTM G77 standard. The results evidence the significant role played by the applied shot peening treatments on wear behaviour of the 6063 aluminium alloy with respect to the as‐received not peened material. The important effect of the surface roughness is also highlighted. The data are discussed on the basis of roughness, surface layer microstructure, microhardness trends and the wear marks observed by means of scanning electron microscopy.

Properties of Metallic Materials after Surface Self Nano-Crystallization

Surface Self-nanocrystallization (SSNC) can produce nanometer grains (10~50μm depth) in the surface layer of metallic materials. And high strength, residual compressive stress as well as a mass of defects attributed to grain refinement and severe plastic deformation, greatly improve their surface properties, such as strength, wear resistance, diffusion property, fatigue performance and corrosion resistance. Now some methods have been confirmed which could realize surface nanocrystallization. This paper reviews the study of surface nanocrystallization and simply summarizes changes in their performance based on surface layer microstructure of metallic materials.

Mossbauer Study of Yttrium Iron Carnet Epitaxial Films Magnetic Microstructure

The magnetic microstructure of the yttrium iron garnet epitaxial films surface layer were studied by conversion electronic Mossbauer spectroscopy method. The presence of two magnetically non-equvivalent positions of Fe3+ ions in tetrahedral sites of garnet structure and a paramagnetic phase formed by Fe2+ ions were fixed. Using the model of mixed magnetic and quadrupole interaction by the diagonalization of the nuclear Hamiltonian matrix the information about the spatial orientation of the cation sublattices magnetic moments was obtained and the components of electric field gradient tensor at 57Fe nuclei in different crystal non-equvivalent positions were calculated.