Hardened Surface Layer Research Articles

Spatial imaging of stratified heterogeneous microstructures: determination of the hardness penetration depth in thermally treated steel parts by laser ultrasound

We introduce an improved non-destructive and non-contact measurement technique for the hardness penetration depth of thermally hardened steel parts based on all-optical laser ultrasound. The hardening of the near-surface region results in a stratified system with layers of different microstructural characteristics caused by changes in grain size. We employ spatially resolved ultrasonic backscattering signals to provide subsurface imaging of the axial and lateral hardness profile. Spatial scans over a range of 30 mm with a lateral step size of 100 μm were obtained within 30 s. We investigated three common steel grades with different microstructural characteristics and hardened layer thicknesses ranging from about 3 to 10 mm. The hardened surface layer and the unhardened core material can be identified. The data evaluation is assisted by a supervised machine learning approach that takes advantage of the spatio-temporal ultrasonic backscattering information. This method also provides an alternative route to define the hardness penetration depth using spatio-temporal scattering characteristics.

Investigation of coordinated behavior of deformation at the interface of Cu–Al laminated composite

To understand the differences between the microstructure and stress states owing to uncoordinated deformation in different regions of a Cu–Al contact interface, the normal stress distribution at the contact interface of the Cu–Al composites and the Al metal adhesion on the peeling surface of the Cu layer are investigated by performing numerical simulations and experimental studies. The results show that the percentage of Al metal adhered to the Cu side gradually increased from the edge to the central region. This is mainly because the central area of the contact interface bore a larger normal stress than the edge position, and when the interface normal stress exceeded 470 MPa, the pressure threshold value required for the extrusion of virgin metal from the surface-hardened layer on the Al side was satisfied. The effect of the initial Cu:Al thickness ratio on the degree of interfacial coordination is investigated, and the degree of coordination of the contact interface was observed to improve and then worsen with the increase in the initial Cu:Al thickness ratio (from 3:9 to 8:4). For composites with a Cu:Al thickness ratio of 4:8, the interface was well coordinated, and the bond strength reached 6.13 MPa, corresponding to a 173.7% improvement compared with the Cu–Al composite with more severe stress concentration (8:4).

Kinetics analysis and enhancement mechanism of aluminum-enhanced plasma nitriding for 42CrMo steel

Aluminum-enhanced plasma nitriding (Al-PN) was developed by a complex treatment of electrolyzing aluminum nitrate and plasma nitriding (PN) for 42CrMo steel; the kinetics and enhancement mechanism was analyzed. Optical microscope and X-ray diffractometer were used to determine the microstructure and phases constituents of the samples. The results show that much thicker case depth is obtained, with hard phases of AlN and FexAl formed in the surface layer by Al-PN treatment, which brings about much harder surface layer and excellent wear resistance. The kinetics analysis shows that the diffusion coefficient is enhanced by Al-PN, and the diffusion activation energy is reduced from 100.531 kJ/mol by PN to 45.177 kJ/mol by Al-PN. The relationship between case depth, temperature T (K) and holding time t (s) is obtained as: dAl-PN = 1.17 × 10−5exp(−5434T)t. (753 K ≤ T ≤ 793 K). Finally, the verification tests confirmed that the developed kinetics agrees quite well with the measured values; therefore, it can be used to predict the case depth for a designed process parameters in practical applications.

Metallic cladding through microwave energy of the mixture of Ni and 15% SiC powder on AISI 304: A green approach in surface engineering

In the present study, an attempt was made to develop surface cladding on AISI 304 steel by utilizing a mixture of Ni and 15% SiC powder via microwave energy. The microwave cladding process on the AISI 304 was carried out in the in-house developed set-up on the microwave. The microwave cladding process was carried out on 900 W with a 2.45 GHz frequency for 120 seconds irradiation time. SEM images showed a uniform cladding layer and cladding surface with SiC wt.% of 15 and irradiation time of 120 seconds. The energy dispersive X-ray (EDX) pattern of AISI 304 cladding surface coating with Ni and 15% SiC. EDX pattern showed the element weight percent of Ni, Fe, Cr, Si, O, and C is 58%, 22%, 4.98%, 5.97%, 1.45%, and 7.6%, respectively. EDX pattern for the cladding layer showed the element's weight percent of Fe, Ni, Si, C, O, and Cr is 46.34%, 27.3%, 11.12%, 7.9%, 4.2%, and 3.14%, respectively. XRD of the cladding surface shows the presence of Fe, FeNi3, NiSi2, Cr2C, Ni3C, Fe2SiO4, and SiC phases. The average hardness of the cladding surface and cladding layer was found to be about 324 HV and 306 HV, respectively. The hardness of the cladding surface was improved by about 46.60%. Fatigue strength of AISI 304 without and with the microwave cladding of the mixture of 15% SiC and Ni powder was found to be 210 MPa and 245 MPa, respectively, at the cyclic load of 1 × 107 cycles. Though, a micrograph of AISI 304 with the microwave cladding of the mixture of 15% SiC and Ni powder shows the fatigue wear, wear debris, and plastic flow of SiC particles after the wear testing.

An Experimental Study of the Influence of Carburizing Treatment Holding Time on the Structure and Hardness of 16NC6 Steel

Low carbon steel with carbon content ranging from 0.15% to 0.3% cannot be hardened through quenching and tempering processes and there is little to no martensitic transformation occurring upon quenching. To improve the surface hardness, carburizing is commonly employed. Through this treatment, the surface composition of the low-carbon steel is altered by the diffusion of carbon, resulting in a hard outer casing with good wear resistance. This work investigates the effect of the carburizing treatment temperature and holding time on the crystallographic structure, hardness, and hardened surface layer dimension of commercial low-carbon steel 16NC6. The steel was carburized at 900°C for different holding times of 1, 2, and 3 hours. After the carburizing and quenching processes, the hardness values and the morphology of the crystallographic structure were measured and characterized.

In Situ Production of B4C and FeV Enriched Composite Surface on Low Carbon Steel by Cast Sintering Technique

A simple and cost effective technique to obtain locally hardened composite layer on cast alloy was previously developed based on advantages of liquid-sintering theory. This methodology provides an opportunity to produce final product with hardened composite layer with good wear resistance during casting process. The current study investigated the effect of combined B4C and FeV substrates on the composite layer properties during in situ cast sintering technique for low carbon steel. Microstructure inspection, XRD phase analysis, chemical composition, thickness measurement and the hardness test on the produced composite layer were conducted. The technique produced up to 640 (±300) µm thick composite layer with maximum hardness of 481 (± 14.6) HV. The hardness of the reinforced surface layer is 3-4 times higher than the base alloy. The increased hardness of composite zone is directly attributed to the presence of the iron boron (FeB), boron vanadium (V2B3) and iron carbide (Fe3C). There were no significant effect of substrate composition on the produced thickness of the composite layer. However, an increase of FeV proportion in the powder mixture leads increased the hardness. The current study is a first attempt to produce locally hardened surface layer on the low carbon steel using simple and cost effective in situ technique with use of relatively inexpensive substrates.

STUDY OF THE STRUCTURE AND PROPERTIES OF THE SURFACE OF HARD ALLOY VK10KS AFTER TWO-COMPONENT ELECTRICAL EXPLOSION TREATMENT WITH SYNTHETIC DIAMONDS

The article presents the results of studies of the VK10KS hard alloy after two-component electroexplosive treatment (EVL) with synthetic diamonds. Aluminum was used as the exploding conductor. The choice of aluminum is based on the experimental data of a number of researchers who note that in order to increase the strength properties of hard alloys at elevated temperatures, it is necessary that particles with a size of hundredths of a micron of ultrafine α-Al2O3 be present in the cobalt binder. Thus, the addition of aluminum to the bond significantly increases the hardness, wear resistance and bending strength. The essence of the EVL is the accumulation of energy by a battery of impulse capacitors up to 10 kJ and its subsequent discharge for 100 μs through a conductor that experiences explosive destruction. In this case, the treated surface is heated and saturated with explosion products, followed by self- hardening due to heat removal to the environment and deep into the material. To increase the hardening effect, a powder sample of synthetic diamond powder AC2 weighing 60 mg was additionally added to the explosion area. It was experimentally revealed that alloying the surface of the VK10KS hard alloy with the products of aluminum electric explosion with a sample of diamond powder did not lead to the formation of a hardened diamond-type layer. During processing, the diamond powder trans-formed into graphite. Despite the fact that the diamond layer was not formed, surface hardening of the VK10KS hard alloy occurred after the electric explosion of diamond powder with aluminum as a conductor. The thickness of the hardened surface layer is about 15 µm with a nanohardness of 24000 MPa, which is 2 times higher compared to the initial state. The increase in hardness is associated with the refinement of phases in the surface layer and the formation of W2C and α-Al2O3 type carbides. The surface roughness of machined carbide inserts does not exceed the values corresponding to the technical requirements.The study of the cobalt binder in the heat-affected zone after two-component EVL found that the cobalt binder is additionally alloyed with tungsten, carbon, aluminum, which are part of the explosive materials and the base. Additional alloying of the cobalt binder will lead to its hardening, which will positively affect the service life of tungsten carbide hard alloys in general.

The efficiency of tumble finishing as a final post-treatment for fatigue enhancement of notched laser powder bed fusion AlSi10Mg

A hybrid post-treatment combining tumble finishing as a final step after shot peening and heat treatment was developed to alleviate the adverse effects of internal and surface defects on the fatigue performance of laser powder bed fusion AlSi10Mg samples. The effects of each post-treatment were investigated individually and synergistically on microstructure, surface morphology and roughness, hardness, residual stresses, porosity, and rotating bending fatigue behavior of V-notched AlSi10Mg samples. The results reveal that tumble finishing can highly reduce surface roughness by 28 and 32% compared to the as-built and heat-treated states while inducing extra surface layer hardening and compressive residual stresses. The hybrid post-treatment of heat treatment + shot peening + tumble finishing significantly increased the fatigue life of the samples by over 500 times higher compared to the as-built series.

Mechanical wounds expedited starch degradation in the wound tissues of potato tubers

Starch degradation occurs rapidly in stressed plants, but it is unclear how starch degradation occurs in potato tubers after they incur mechanical wounding. In this study, we found that wounding significantly upregulated the expression levels of StGWD, StAMY, StBAM, and StISA, and decreased the starch content of potato tubers. Meanwhile, wounding markedly upregulated the expression levels of StSUS, StBG, and StINV genes, and increased the content of sucrose, glucose, and fructose. Furthermore, wounding reduced the proportion of small starch granules and increase that of large as well as medium starch granules, in this way enhancing the average size distribution of starch. Initially, the hard surface layer of starch granules was removed by wounding, but the internal channels and other structures were only slightly affected. Taken together, the results show that wounding can accelerate starch degradation by promoting the accumulation of sucrose, glucose, and fructose, and the hydrolysis of starch granules in potato tubers.

Analogy test rig for the generation of tooth flank fractures at large gears (WZL-double pulsator)—commissioning and first test results

As a result of the enhanced of load-carrying capacity with regard to pitting and tooth root breakage, generation of tooth flank fractures became more frequent. This type of damage differs from existing fatigue damages on the tooth flank in that crack initiation takes place below the case hardened surface layer and the tooth breaks in the area of the active tooth flank. An isolated investigation of tooth flank fractures is currently not possible because there is no analogy test rig available that can reproduce both, the compressive stress due to Hertzian contact flattening as well as the tensile stress due to tooth bending. For this reason, a test rig concept is being developed, manufactured and put into operation in the DFG research project “Analogy test rig for tooth flank fractures”, which allows the generation of tooth flank fractures in absence of other damage types. This report deals with the commissioning of the WZL-Double Pulsator as well as first test results. The FE model of the analogy test rig is validated by measuring tooth root strains with strain gauges and comparing them with the calculated strains. Finally, the commissioning is carried out and first tests are performed.

A comprehensive study on the fatigue properties of duplex surface treated Ti6Al4V by plasma nitriding and DLC coating

This study aims to investigate the effects of duplex surface treatment consisting of plasma nitriding and DLC coating on the fatigue properties of Ti6A4V alloy. For this investigation, Ti6Al4V samples were plasma nitrided at 650 °C, 700 °C and 750 °C for 1, 2 and 4 h and then DLC films were produced on the plasma nitrided samples. The structural, mechanical and morphological features of the samples were characterized by XRD, SEM, micro hardness tester and scratch tester. Fatigue tests were performed on the samples by using stress life method. On the surface and sub-surface of the samples, a compound layer and a diffusion zone were formed by plasma nitriding, respectively and XRD results revealed that these layers consisted of Ti2N and TiN phases. The raising process time and temperature caused to increase the thickness of these layers and they also increased the surface hardness of the samples. On the other hand, DLC coated samples exhibited more surface hardness than untreated and all the plasma nitrided samples. Fatigue analyses revealed that plasma nitriding reduced the fatigue strength of the material in all process conditions. Although plasma nitriding formed hard surface and sub-surface layers, the brittle structure of the layers and the great difference of elastic modulus between the substrate and nitride layers caused to decrease the fatigue strength of the material. Although DLC coating increased the fatigue strength of untreated and plasma nitrided samples at 650 °C for 1 h, 700 °C and 750 °C for 4 h), the fatigue strength of duplex treated samples (plasma nitrided at 650 °C for 1 h, 700 °C and 750 °C for 4 h and DLC coated) was lower than the fatigue strength of untreated material, similar to only plasma nitrided materials. This showed that the fatigue strength of duplex treated Ti6Al4V was controlled by plasma nitriding.

Surface Characteristic and Friction Behavior of Plasma Sprayed FeCoNiCrMo0.2 High Entropy Alloy Coatings on BS960 High-Strength Steel with Subsequent Shot Peening Treatment

The FeCoNiCrMo0.2 high entropy alloy coatings were deposited on BS960 high strength steel by plasma spraying method with four different current intensities (250 A, 350 A, 450 A, 550 A). These coatings were then subjected to a subsequent micro-shot peening treatment. Surface characteristics including surface morphology, microhardness and phase composition were characterized, and the wear resistance of the coatings was assessed by reciprocal friction and wear tests. The results showed that the high entropy alloy coatings had FCC structure. XRD results showed that no new phase was formed during the spraying process. At the same time, shot peening treatment could effectively improve the hardness of the coating surface. Under the four processes, the coating surface prepared with the current intensity of 350 A had the highest microhardness and uniformity before and after shot peening, and the hardness values were 473 ± 10.21 and 504 ± 8.62 HV0.2, respectively. The friction and wear test results showed that the friction coefficients of the four coatings were close to each other at 10 N load, which was about 0.4. When the test load reached 25 N, the friction coefficient of the coating with current intensity of 350 A was lower, and it showed better friction performance. After shot peening, the friction coefficient of the four coatings further decreased to about 0.3 under 10 N loading due to the existence of hardened surface layer. When the test load reached 25 N, the hardened layer would be worn through and the friction coefficient would suddenly rise. Under the 25 N test load, the hardened layer of the high-entropy alloy coating with current intensity of 350 A illustrated better friction resistance.

Monitoring cheese ripening by single-sided nuclear magnetic resonance

The noninvasive, longitudinal study of products and food processing is of interest for the dairy industry. Here, we demonstrated that single-sided nuclear magnetic resonance (NMR) can be used for noninvasive monitoring of the cheese ripening process. The maturation of soft-ripened Camembert-like molded cheese samples was monitored for 20 d measuring 1-dimensional and 2-dimensional NMR relaxation and diffusion data at various depths, ranging from the hard surface layer to the soft center. Gelation and gel shrinkage were observed throughout ripening, and a complete loss of free water signal was observed at the cheese rind. Transversal (T2) relaxation distributions include 3 components that evolve with ripening time and position, corresponding to water inside the casein gel network, water trapped in casein, and fat. Two-dimensional T1-T2 relaxation experiments provided enhanced resolution of the 3 components, allowing quantification of the relative proportions of each phase. Furthermore, diffusion (D)-T2 relaxation correlation experiments revealed the bimodal size distribution of fat globules. The study demonstrated that single-sided NMR can provide spatially resolved signal intensity, relaxation, and diffusion parameters that reflect structural changes during the ripening process and can be exploited to understand and monitor the ripening of cheeses.

Improved tensile strength and fatigue properties of wire-arc additively manufactured 2319 aluminum alloy by surface laser shock peening

Wire-arc additive manufacturing (WAAM) has been extensively studied thanks to its high material utilization rate and ability to form large-size components. However, due to the considerable internal porosity, the as-build (AB) parts usually exhibit poor tensile and fatigue properties. In this study, laser shock peening (LSP) was applied as a post-treatment method on WAAMed 2319 aluminum alloy. By performing LSP on the surfaces of the material, an influencing layer with a thickness of 1.3 mm was generated. The peak hardness and yield strength increased by 30.2% and 151.2%, respectively. Under the action of concentrated compressive residual stress (CRS) around the pore defects, the number density of pores is reduced by 65.3%, while collapsed large-size pores were observed. The combined effect of CRS, surface hardening layer, and defect reduction doubles the fatigue life. The “Ladder” like mutation was observed in the failure process, and its formation can be attributed to the resistance between pores and CRS.

KINETICS OF DESTRUCTION AT THE SURFACE STRENGTHENING OF MACHINE PARTS

Studying the influence of various factors on the strengthening effect and the kinetics of destruction of surface-hardened parts under cyclic loading is important for strength and durability calculations. A curve is indicated that characterizes the distribution of residual stresses after surface hardening of a part. The diagrams obtained in the work were constructed as a result of algebraic summation of the original diagrams. The analysis performed makes it possible to explain the nature of the crack occurrence: a crack nucleates under certain conditions under a surface-hardened layer in the core material of the part in a half-cycle of tensile stresses from an external load. The research was carried out on samples made of steel 45 with a boron-chromed diffusion layer obtained by successively saturating the surface with boron and chromium.

Формирование упрочненного поверхностного слоя при лазерной резке шестерен зубчатых передач из конструкционной легированной стали марки 40X

Формирование упрочненного поверхностного слоя при лазерной резке шестерен зубчатых передач из конструкционной легированной стали марки 40X

Structural changes in steel during hardening by deformation wave

The article presents results of study possibility of hardening of high-manganese steel X120Mn12 by a deformation wave in the process of wave strain hardening (WSH). Features of the method is possibility of using shock waves for plastic deformation, which significantly expands the technological capabilities for formation of a hardened surface layer. The dominant design and technological parameters of the hardening treatment are established, which have the main influence on the microstructure and hardness of the hardened surface layer. Possibility of a significant increase in hardness and depth of hardened surface layer is established. The depth of hardened layer can reach 6-8 mm, and the hardness can be increased by more than three times. Microstructural analysis showed no cracks. The obtained results of conducted research can be used to develop a technology for strengthening the deformation wave of various heavy-loaded parts made of high-manganese steel.

Study of topography of surface layer of structural steel subjected to electromechanical coining

The results of studies of the formation of a discrete structure of a hardened surface layer of normalized steel 45 after electromechanical processing with the dynamic application of a deformation force (electromechanical chasing EMC) are presented. The influence of the treatment current density on the macrogeometry, structure and microhardness of surface-hardened steel specimens has been established. It is shown that EMС allows creating discrete structures on the treated surface, consisting of hardened and non-hardened metal zones with various topography. The main dependences are given that connect the characteristics of discrete structures of different topography with the parameters of the electromechanical coinage mode. The results obtained can be used to provide a targeted distribution of physical and mechanical properties in the surface layer after EMС depending on the specific operating conditions of the parts.

Laser heat treatment effect on fatigue of hinged cantilever beams

The paper considers the effect of laser hardening treatment of steels on the fatigue strength of materials. The statement of efficiency of laser processing for formation of hard surface layer of processed surface which protects from wear is substantiated in relation to a hinge design in agricultural machines placed on a cantilever fastened beam which is a hinge axis. The phenomenon of reduction of fatigue characteristics of structural steels after laser treatment is investigated. Influence of fatigue loading on beam durability is analyzed. On the basis of experimental data analysis, the conclusion is formulated that the surface defects in the form of wells which are formed under the influence of laser pulse play an important role during the pulse laser treatment. Particular attention is paid to the role of residual stresses generated by the thermal effects of the laser. On the basis of this research, it is recommended that laser hardening treatment should be carried out, the pulse energy of which does not lead to surface melting.

Establishing the causes of premature damage of steam turbine rotor blades of TPP

The technical condition of the metal of the steam turbine blade was analyzed and the reasons for its fracture were established. It was shown that the relative elongation δ of the blade metal varied from 7.4 to 11.5%, and was lower than the regulated level. The low values of δ and the obtained values of the ratio between yield strength and ultimate tensile strength σYS / σUTS, which varied from 0.8 to 0.89, indicate a low margin of plasticity of the blade metal, which contributed to its cracking under the action of working loads. Metallographic analysis revealed pores in the surface-hardened layer of the blade. They caused low adhesion of the layer with the base metal of the blade, and also of crack initiation. The high stress concentration and the contact of the blade metal with the working medium contributed to the growth of a subcritical corrosion-fatigue crack in the cross-section up to its complete destruction.