Low Alloy Steel Substrates Research Articles

Electrochemical synthesis of vanadium boride powders from their oxide salts

A novel environmentally friendly electrochemical method for synthesizing vanadium boride powders from oxide-based electrolytes was introduced. During this process, co-depositions of vanadium and boron atoms took place on the surface of the low alloyed steel substrates at various stoichiometries, VxBy (x≥1; y≥1). The effects of critical electrolysis parameters namely current density (70, 100, 200, 500 mA/cm2), and temperature (900, 950, 1000 °C) were investigated systematically. The X-ray diffraction (XRD) analyses revealed that at low current density (70 mA/cm2) VB is the main phase; whereas, VB2 became a dominant structure at 100 and 200 mA/cm2. However, at high current densities like 500 mA/cm2 mixed borides containing VB- V3B4- V2B3 -VB2 were detected. The electrolysis temperatures did not cause major variations in the composition of synthesized borides. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) as well as grain size investigations indicated that there is no significant influence of electrolysis conditions on the particle size and it is possible to manufacture high-quality, stoichiometric VB, and VB2 powders with ≈ 4 µm particle size. The best parameters for producing powders containing primarily VB and VB2 powders were determined as 1000 °C, 70 mA/cm2, and 900 °C, 200 mA/cm2, respectively.

Corrosion study of glass coated high strength low alloy steel

In the present study, the glass slurry coating to a high-strength low-alloy steel (HSLA) substrate was investigated for corrosion resistance material. The crystallographic phases, degree of crystallinity, lattice parameters, and potential changes due to the coating process, and microstructural changes such as visual inspection of the surface, revealing thickness, uniformity, adhesion, potential defects, and elemental composition of the bare and coated steel were investigated by using the X-ray diffraction (XRD) and scanning electron microscopy and electron dispersive spectroscopy (SEM/EDS). The electrochemical behavior of the bare and coated steel samples was compared using potentiodynamic polarization and electrochemical impedance spectroscopy at various immersion periods in a 3.5 wt.% of sodium chloride (NaCl) solution. The higher corrosion resistance and lower corrosion rates of the coated steel surfaces were observed. The protection effectiveness of coatings is evaluated by examining their impedance and polarization characteristics. The effectiveness of the glass coatings in inhibiting corrosion is attributed to their role as a physical barrier and their ability to release corrosion inhibitors into the surrounding electrolyte. This information can be crucial for real-world applications requiring corrosion resistance.

Grinding- and robotic hammer peening-induced modifications in the near-surface regions of laser-cladded Inconel 718 coatings

Inconel 718 coatings deposited by laser-cladding (LC) on low-alloy steel substrate have been grinded followed by robotic hammer peening (RHP). White layer consisted of nanograins, smaller than 100 nm, has been observed on the surface accompanied with a deformation layer underneath after grinding and RHP. By increasing the RHP intensity (i.e., both the impact energy and the dent overlap), the residual tensile stress measured by X-ray diffraction from the surface of the coating has been monotonically reduced and eventually converted to residual compressive stress with increased in-plane anisotropy, which was accompanied with monotonically increased surface hardening up to 40.5 HRC. Grain deformations have been induced in the white- and deformation-layer, they are dominated by twinning and slipping, respectively. In terms of depth-dependent distributions of low-angle (<15°) grain boundaries and hardening, the effective cold-working thickness induced by the RHP process is over 1000 μm, which is close to the thickness of a single-pass LC deposition. Onset of porosity closures occurred upon the RHP process, especially in the near-surface regions. These findings shed light on integrity enhancement for additive manufacturing of metal alloys by LC-based techniques through introducing interpass RHP process.

Microhardness and Elastic Properties Evaluation of WC-TiC Coatings Obtained by Arc Spraying Process

Fulfilling the basic role of hard thermal sprayied coatings is closely related to the value of its microhardness. The quality of such a layer depends on several variables, the main categories being: spray method (flame spray, electric arc, plasma spray, cold spray, etc.), spray parameters (spray distance, voltage and intensity, working atmosphere, direction of the spray jet, etc.) and the materials used (chemical composition of the coating materials, quality and texture of the substrate). In this study, the microhardness, elastic properties and cohesion of a coating made of hard cored wire (Praxair – Tafa) by electric arc spraying process on a low alloy steel substrate, were analyzed. The cored wire has as main hard elements WC (about 26%) and TiC (about 6%), the rest of the chemical elements present being: Cr (14%), Ni (4.5%), B (1.87%), Si (1.25%) and the Fe balance. The micro-hardness was evaluated onto the surface of the coating, previously prepared by grinding to reduce the as-coated roughness. The method based on recording the forcess generated during the indentation with simultaneous measurement of the load – depth curve (with UMT 2MCETR microtribometer) were used for the microhardness evaluation. In order to analyse the cohesion of the coated layer, scratch tests with progressive loading (10N, 15N and 20N) were performed on the same microtribometer. Tests have shown that the metal matrix uniformly includes the hard particles arised from the core of the wire, and at the microstructural level, the microhardness varies significantly, depending on the hardness of the particles on which the indentor tip applies the loading forces. However, the overall behavior of the coatings thus realized is a satisfactory one, being, as a general behavior, in the average required by the applications of such a layer.

Thermal-induced evolution of microstructure as a plasma arc coating Direction-Dependent phenomenon

This study elucidates the effects of different directed energy deposition trajectories on the microstructure and properties of powder plasma transferred arc welding (PPTAW) fabricated coatings. Two trajectories, straight (STT) and complex (CXT), were explored to deposit NiCrBSi powders onto a low alloy steel substrate. Finite element thermal analysis revealed distinct heat distribution zones, the middle zone (MZ) and transition zone (TZ), showing temperature variations between the STT and CXT coatings. Microstructural examination indicated lower dendrite arm spacing (DAS) in the STT coating (11 μm) than in the CXT coating (16 μm). Electron backscatter diffraction (EBSD) analysis demonstrated significant grain refinement in the STT coating (17.4 μm) versus the CXT coating (68.7 μm). X-ray diffraction phase analysis identified three reinforcing phases − γ-Ni, Cr23C6, and Cr3C2 – enhancing corrosion resistance and tribological properties. The STT coating exhibited superior corrosion resistance with a corrosion current density (icorr) of 12.8 µA/cm2, while the CXT coating showed icorr of 34.3 µA/cm2. Additionally, the STT coating exhibited higher hardness (832 ± 33 HV1.0) and better wear resistance with a wear rate of 10.46 ± 0.29 × 10-3 m3/m, over the CXT coating (hardness: 450 ± 36 HV1.0; wear rate: 12.67 ± 0.54 × 10-3 m3/m).

Surface Characteristics of Vacuum-Plasma-Sprayed Reinforced Stainless Steel Coatings with TiC Particles

Fe-based coatings reinforced with TiC particles exhibit outstanding properties and are widely recognized as highly promising coatings or components with superior performance. In the present study, composite materials using a powder mixture of AISI 316 stainless steel and TiC particles were deposited by vacuum plasma spraying onto a S235 low alloyed steel substrate. The coating and the base material were characterized in terms of microstructure and surface properties. The metallographic analysis of the deposited coating revealed the uniform distribution of the TiC into the stainless steel matrix. The results show that the presence of tungsten carbide particles improved the hardness and tribological properties of the composite coating compared with the S235 base material. The wear resistance of the coating was approximately seven times higher than that of the low alloyed steel substrate. The electrochemical corrosion resistance of the coating in chloride media was much higher than that of the base material.

Microstructural Evolution of High-Entropy Intermetallic Compounds during Detonation Spraying

This study aims at investigating the feasibility of depositing quality coatings from various high-entropy intermetallic compounds (HEICs) using detonation spraying (DS). Four different HEIC coatings, namely (NbTaVCrTi)Al3, (NbTaVNiFe)Al3, (NbTaVZrHf)Al3, and (FeNiCoCrMn)(MoCr), were prepared by DS on low alloy steel substrates. The HEIC powders were first prepared by arc melting followed by ball milling and then used as reinforcement particles to deposit HEIC coatings. Elemental segregation was observed for all the as-cast samples. Powders with average particle sizes of about ~25 µm for (NbTaVCrTi)Al3, ~22 µm for (NbTaVNiFe)Al3, ~34 µm for (NbTaVZrHf)Al3, and ~18 µm for (FeNiCoCrMn)(MoCr) were obtained. (NbTaVCrTi)Al3, (NbTaVNiFe)Al3, and (NbTaVZrHf)Al3 HEICs exhibited a nearly single D022 (TaAl3 type) structure, while (FeNiCoCrMn)(MoCr) exhibited a single D8b (FeCr type) structure. Dense coatings consisted of a lamellar microstructure and sound bonding with the substrate, and low porosity was obtained for all the samples. Crystal structures of the HEIC samples were highly retained during DS, whereas all the samples underwent some degree of oxidation. Microhardness values of 745 HV for (NbTaVCrTi)Al3, 753 HV for (NbTaVNiFe)Al3, and 862 HV for (NbTaVZrHf)Al3 were obtained, which are significantly higher than the microhardness of the substrate (~140 HV). Among all the samples, (FeNiCoCrMn)(MoCr) exhibited the highest microhardness values of about 1047 HV.

Detonation Spraying of Ni-Based Composite Coatings Reinforced by High-Entropy Intermetallic Particles

Ni-based composite coatings reinforced by high-entropy intermetallic compounds (HEICs) were prepared by detonation spraying (DS) on low alloy steel substrates. To this end, first (Ti-Nb)(V-Cr-Ni-Fe) and Al3(TiZrNbCrHfTa) HEIC powders were fabricated by arc melting followed by ball milling. The as-milled HEIC powders were then employed as reinforcement particles to prepare Ni-7wt.% HEIC composite coatings. The average particle size of the (Ti-Nb)(V-Cr-Ni-Fe) and Al3(TiZrNbCrHfTa) HEIC powders were 18 and 35 µm, respectively, while the average particle size of the Ni powder was 56 µm. (Ti-Nb)(V-Cr-Ni-Fe) exhibited a single hexagonal C14 Laves phase in spite of Ti and Nb segregations. The XRD pattern of Al3(TiZrNbCrHfTa) indicated the presence of a tetragonal D022-type structure along with some minor CrTi and Cr5Al8 phases. The sprayed Ni-7wt.% FeNiCrV-TiNb and Ni-7wt.% Al3(TiZrNbCrHfTa) composite coatings retained crystal structures of the powder mixtures, suggesting proper thermal stability for both powders. The coatings exhibited a dense microstructure consisting of a lamellar microstructure with low porosity and sound bonding with the substrate. The microhardness of Ni-7wt.% FeNiCrV-TiNb (450 HV) was higher than that of Al3(TiZrNbCrHfTa) (338 HV), and it exhibited lower fluctuation than that of Ni-7wt.% Al3(TiZrNbCrHfTa). DS is an effective method to fabricate metal matrix composites reinforced by HEICs with a low level of porosity.

Research on Thermal Properties and High Temperature Exposure Behavior of Non-Skid Coating Fabricated by Twin Wire Arc Spraying

Conventional non-skid coatings for marine construction contain polymeric materials. These materials are generally susceptible to high temperature environments because of their low thermal conductivity and thermal resistance. A metal-based non-skid coating has great potential for high temperature applications, yet, there has only been limited research. In this study, twin wire arc spray (TWAS) was used to fabricate Al and Al-3%Ti coatings on a high strength low alloyed (HSLA) steel substrate. The purpose of this study is to confirm the feasibility of TWAS Al-based coating for non-skid areas on marine construction. The static coefficient friction of TWAS Al-based coatings exhibited excellent and uniform values compared with a conventional epoxy-based non-skid coating. The specific heat and thermal conductivity of TWAS Al-based coating was measured and compared with that of the substrate. The thermal property values of the TWAS Al-based coating were reported for the first time in this study. The TWAS Al-based coating had A continuous interface with the substrate and the general microstructural features of a thermal-sprayed metal coating. After exposure to 500℃ for 24 hours, the an Fe-Al intermetallic compound and oxide were formed inside of the coating and coating-substrate interface. The adhesion strength indicated that the TWAS Al-based coating sustained its strength after the isothermal exposure test. The Vickers hardness of the TWAS Al-3%Ti coating was higher than that of the Al coating. The solid solution hardening of Ti atoms in the as-deposited coating and the precipitation hardening of the TiAl3 compound in the heat-treated coating contributed to the improvement of in Vickers hardness. Thus, the TWAS Al-3%Ti coating is proven to be a promising nonskid coating for high temperature applications.

Microstructure and Wear Resistance of High-Chromium Cast Iron with Multicomponent Carbide Coating via Laser Cladding

High-chromium cast iron (HCCI) coatings with multicomponent carbides were prepared on low-alloy steel substrates using a laser cladding technique in this work. The microstructure and wear resistance of the coatings were characterized via optical microscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, X-ray diffraction and block-on-ring wear testing. Multicomponent carbides (Ti, Nb, Mo, W, V)C with an FCC structure and multicomponent compounds (Nb, Mo, W, V) (B,C) with an FCC structure were found in the microstructures of coatings after multielement doping. In addition, (Cr, Mo, W, V)23C6 compounds could be obtained by heat treatment. These multicomponent compounds were beneficial for obtaining coatings with an excellent hardness (60 HRC) and high wear resistance. This multielement doping method provides an effective modified method for preparing high-wear-resistance laser cladding coatings.

Corrosion-resistant thermal spray coatings for low-alloy steel in contact with molten nitrate salts in solar power plants

The longevity and the cost of thermal energy storage (TES) components in solar power plants is a matter of great concern. To address this issue, three kinds of thermal spray coatings (Ni-5Al, NiCoCrAlY, and CoNiCrAlY) were successfully deposited on the low-alloy steel (P91) substrate by high velocity oxygen fuel (HVOF) spraying process. The corrosion performance of the prepared coatings in Solar Salt (at 565 °C for 15 days) was evaluated in detail by gravimetric analysis, field emission scanning electron microscopy (FESEM), and X-ray diffraction (XRD). Results revealed that all three coatings were quite dense and the substrates were generally well protected by the coatings. Compared with Ni-5Al and NiCoCrAlY coatings, the CoNiCrAlY coating exhibited the best corrosion performance owing to the formation of a dense oxide layer on the surface. Further, it was revealed that despite containing corrosion-resistant composition in NiCoCrAlY coating, the presence of a large number of phase interfaces could be the vulnerable regions that may result in local corrosion failure. Moreover, increasing the content of aluminum and using pre-alloyed powder may be an excellent solution to improve the performance of Ni-5Al coating.

Comparative Research on Corrosion Resistant Non-Skid Al and Al-3%Ti Coating Fabricated by Twin Wire arc Spraying

To ensure the lifetime of marine constructions and the safety of workers and pedestrians, corrosion protective non-skid coating is an effective solution. However, the conventional polymer-based coating has some limitations. In this study, newly-suggested Al and Al-3%Ti coatings were deposited on high strength low alloyed steel substrate using twin wire arc spraying (TWAS). The static and dynamic friction coefficients of the Al-based coatings under dry and wet conditions were measured using portable friction testers. To evaluate the corrosion behavior under sea water conditions, a cyclic potentiodynamic polarization test (CPDP) and salt solution immersion test (SSIT) were performed with a 3.5% NaCl solution. To confirm the coating degradation, mechanical properties (Vickers hardness and adhesion strength) were compared before and after SSIT. The results showed that the TWAS Al-based coatings were well fabricated on HSLA steel and had the general microstructure of a thermal spray. The coatings provided excellent corrosion protection for the steel substrate and greatly increased the friction coefficient of the surface. The Vickers hardness slightly increased and adhesion strength decreased after SSIT. The microstructure observation revealed that the TWAS coatings had a bimodal structure induced by non-uniform droplet generation at the TWAS tips. After SSIT, some oxides formed on the surface and porous regions of the coatings. This indicated that the TWAS coating successfully provided corrosion protection and non-skid properties.

Evaluation of abrasive wear resistance of self-fluxing Ni-base coatings by scratch testing

"Abrasion wear is one of the most dominant types of wear in many applications, causing over 50% of all wear failures [1]. The abrasive wear phenomenon could be classified regarding several aspects: a) the position of the abrasive particles: two-body abrasion if they are fixed, or three-body abrasion if they are free to slide and/or roll, b) the stresses involved: gouging abrasion, high-stress abrasion (grinding) and low-stress abrasion (scratching), c) the surface appearance: ploughing, cutting, fatigue and fracture (cracking). In this study was approached the possibility of abrasion wear resistance evaluation of selffluxing Ni-base coatings by scratch testing. Materials used in tests were: three self-fluxing Ni-base coatings deposited on low-alloyed steel substrate using flame spraying process (referred to as S1, S2 and S3). The wear of the samples and the friction coefficient were investigated with scratch tester and analyzed in correlation with their mechanical properties. "

Pitting corrosion – Preferred chloride diffusion pathways in physical vapor deposited AlCrN coatings

Pitting corrosion of sputtered and arc evaportaed fcc-AlCrN coated low-alloy steel substrates was studied in a 0.1 M NaCl solution, using a three-electrode-cell. Depending on the deposition technique, several diffusion mechanisms were identified by high-resolution techniques (i.e. APT, TOF-SIMS). For arc evaporated AlCrN, incoherently embedded macro-particles provided the majority of fast-track diffusion pathways and pit-initiation sites, while their pristine coating matrix proved protective against chloride inward diffusion. Contrarily, the more coarse-grained sputtered AlCrN morphology with a highly orientated crystal growth featured diffusion paths along column boundaries, where chloride permeated the coating structure and initiated pit formations at the coating-substrate interface.

Effect of longitudinal magnetic fields on the grain growth of hollow stud welded joints

In this study, a drawing arc stud welding method combined with a longitudinal magnetic field was used for welding a 30CrNi3MoV low-alloy super strong steel substrate and Q235 hollow steel, and the effects of a longitudinal magnetic field on the microstructure growth process and mechanical properties of stud welds were studied. The results show that an arc controlled by a longitudinal magnetic field stirred the molten pool continuously, reducing the number of coarse proeutectoid ferrite, increasing the proportion of acicular ferrite, and smoothing the transition of alloyed elements near the weld joint fusion line within a certain range of excitation current. Under the action of the magnetic field, the weld grain size was refined from 4.30 μm to 3.14 μm, and the proportion of large-angle grain boundaries in the weld area increased from 24.27% to 34.2%. After the magnetic field application, the toughness of the welded joint was significantly improved. With an increase in the excitation current, the shear strength of the joint first increased and then decreased to 312 Mpa. Similarly, the impact toughness of the joint first increased and then decreased to 31.88 J·cm−2

Direct deposition of low-cost carbon fiber reinforced stainless steel composites by twin-wire arc spray

Metal matrix composites (MMCs), combining the unique advantages of two or more constituents, have been recognized as a promising structural material system. Particularly, MMCs reinforced by carbon fibers (CFs) have opened new material design routes towards increased strength-to-weight ratios. Here, we demonstrate a low-cost one-step deposition of CF reinforced stainless steel (CFRSS) composites by twin-wire arc spray on low-alloy steel (LAS) substrates. The CFs are self-assembled and grow coherently, up to 100 s of μm in length, along the splat-domain boundaries with enhanced bonding to their vicinals through partial oxidation. Structural and electrochemical studies reveal a pitting corrosion of the CFRSS layer in aqueous NaCl (3.5 wt.%) electrolyte and the corrosion passivation is apparently larger than that of the LAS substrate. Both the micro- and nano-hardness of the CFRSS layer are improved to over 4 times higher than that of the LAS substrate. These property enhancements indicate that this low-cost one-step process could revolutionize protective coatings on LAS against corrosion and/or erosion under aggressive conditions.

High entropy intermetallic coatings fabricated by detonation spraying

(Co1/3Fe1/3Cu1/6Ni1/15Mn1/10)Al and (Cu1/4Fe1/4Ni1/4Ti1/4)3Al high entropy intermetallic compound (HEIC) coatings were deposited on low alloy steel substrate by detonation spraying (DS) using pre-alloyed powders. The (Co1/3Fe1/3Cu1/6Ni1/15Mn1/10)Al and (Cu1/4Fe1/4Ni1/4Ti1/4)3Al HEIC powders fabricated by induction melting followed by ball milling had a single B2-ordered and a double B2 + FCC phase structures, respectively, which exhibited excellent stability during DS. The coatings exhibited sound bonding with substrate, and consisted of lamellar microstructure with low porosities. DS is anticipated to be a high throughput technique to fabricate HEIC coatings with dense microstructure for use in different industries.

Cracking behavior and formability of Zn-Al-Mg coatings: Understanding the influence of steel substrates

Zn-Al-Mg coatings are important materials for the corrosion protection of steel sheets. However, susceptibility towards cracking limits the formability performance of these coatings. In this study, we focus on the effect of the underlying steel substrate on cracking behavior in these coatings. In order to elucidate this, a high-strength low-alloy (HSLA) steel substrate and an interstitial-free (IF) steel substrate are coated with two different ZnAlMg coatings with and without binary eutectic microstructures. Meticulous in-situ tensile and bending tests are conducted in a scanning electron microscope. To quantify the strain distribution and damage incidents, micro and macro digital image correlation techniques are utilized in order to illuminate the associated cracking causes across length scales. Furthermore, electron backscatter diffraction method is applied to study the role of crystallographic orientation on the cracking tendency. Crack opening and crack area fractions are correlated with the applied strain and bending angles. The findings denote that the discontinuous yielding (Lüders banding) of the HSLA steel substrate generates substantial surface roughening and heterogeneous deformation in the coatings that facilitates cracking. In contrast, the IF steel induces a more uniform deformation within the coatings leading to much reduced crack size and crack area fraction. This study has resulted in a key element of a guideline towards crack-resistant and formable Mg-alloyed zinc coatings.

Matrix Composite Coatings Deposited on AISI 4715 Steel by Powder Plasma-Transferred Arc Welding. Part 3. Comparison of the Brittle Fracture Resistance of Wear-Resistant Composite Layers Surfaced Using the PPTAW Method.

This article is the last of a series of publications included in the MDPI special edition entitled “Innovative Technologies and Materials for the Production of Mechanical, Thermal and Corrosion Wear-Resistant Surface Layers and Coatings”. Powder plasma-transferred arc welding (PPTAW) was used to surface metal matrix composite (MMC) layers using a mixture of cobalt (Co3) and nickel (Ni3) alloy powders. These powders contained different proportions and types of hard reinforcing phases in the form of ceramic carbides (TiC and WC-W2C), titanium diboride (TiB2), and of tungsten-coated synthetic polycrystalline diamond (PD-W). The resistance of the composite layers to cracking under the influence of dynamic loading was determined using Charpy hammer impact tests. The results showed that the various interactions between the ceramic particles and the metal matrix significantly affected the formation process and porosity of the composite surfacing welds on the AISI 4715 low-alloy structural steel substrate. They also affected the distribution and proportion of reinforcing-phase particles in the matrix. The size, shape, and type of the ceramic reinforcement particles and the surfacing weld density significantly impacted the brittleness of the padded MMC layer. The fracture toughness increased upon decreasing the particle size of the hard reinforcing phase in the nickel alloy matrix and upon increasing the composite density. The calculated mean critical stress intensity factor KIc of the steel samples with deposited layers of cobalt alloy reinforced with TiC and PD-W particles was 4.3 MPa⋅ higher than that of the nickel alloy reinforced with TiC and WC-W2C particles.

Microstructure and Wear Behavior of Microwave Treated WC-10Co-4Cr Composite Coating on AISI 4140 Alloy Steel

WC-10Co-4Cr composite coatings have been coated with AISI 4140 low alloy steel substrate using high-speed oxygen fuel (HVOF) technology with a particle size from 0 to 50 microns. Microwave heating energy is used to enhance the mechanical and tribological properties of sprayed coatings as post-heat treatment technique. Microwave fused coatings exhibit greater surface roughness, porosity, micro hardness, and wear strength than the as sprayed deposition. The as coated and fused coatings have been characterized by x-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) procedure. Wear behaviors under normal loads of 5N, 10N and 15N have been investigated by a pin on a disc device at temperatures of 30 °C, 100 °C and 200 °C. The results revealed that microwave-treated coatings are highly recommended to protect the sliding surface, such as a high-speed spindle, under different environmental conditions.