Equiaxed Crystals Research Articles

Effect of residual stress and phase constituents on corrosion-cavitation erosion behavior of 304 stainless steel by iso-material manufacturing of laser surface melting

Different from additive manufacturing and subtractive manufacturing, iso-material manufacturing (also named isovolumetric manufacturing) is applied to 304 stainless steel (304SS) by laser surface melting (LSM) at four energy density (51 J/mm2, 44 J/mm2, 39 J/mm2, 37 J/mm2), aiming at improving the resistance to corrosion and cavitation erosion without any addition of precious metals. The experimental results show that the microstructure presents the transformation from plane crystal → columnar crystal → equiaxed crystal from interface to top surface. All the samples exhibit austenite+martensite+Cr23C6, and the martensite content is increased from 9.3% to 40.8% with the energy density decreasing after iso-material manufacturing. In addition, low angle grain boundary is increased, and nano-mechanical properties also show an increasing trend. The decreasing of energy density also enhances the residual tensile stress of the melting layer. The sample obtained at energy density of 51 J/mm2 displays the highest corrosion resistance in 3.5 wt% NaCl solution, which can be attributed to its low galvanic corrosion degree and small residual tensile stress. The sample obtained at energy density of 39 J/mm2 exhibits the highest cavitation erosion resistance (Re) and its passivation film displays better self-repairing and re-passivation ability as indicated by synergistic cavitation erosion-corrosion behavior. The high cavitation erosion resistance can be attributed to the proper compromise of the constituent phases and higher self-repairing of the passivation film for the melting layer. Moreover, the 304 stainless steel prepared in this study exhibits a high or comparable corrosion and cavitation erosion resistance in comparison with the samples prepared by other fabrication method reported previously.

A novel directed energy deposition-arc method of deposition layer without focused thermal energy heating: droplet transfer, morphology and microstructure

Additive manufacturing (AM) of metal usually forms columnar grains along the building direction due to the focused thermal energy directly heating the deposition layer to easily obtain an obvious temperature gradient. The columnar grains are not conducive to AM-sample application, which results in the property anisotropy of the AM-sample. In this work, a novel directed energy deposition-arc (DED-Arc) method for depositing layers without direct heating by focused thermal energy is proposed. The arc burns between the tungsten electrode and a water-cooled electrode, were only used to melt the wire during DED-Arc process. Using stainless steel wire as a model alloy, by studying droplet transfer, morphology of the deposition layer and microstructure evolution, the feasibility of the method was fully verified. Two kinds of droplet transfer modes were observed, and the difference between them was whether the droplet contacted the molten pool before falling off. The focused thermal energy is only used to melt the wire, and the droplet transfer cycle is mainly affected by gravity, greatly decreasing the heat accumulation compared with existing methods. The heat-affected zone (HAZ) was obviously inhibited. The grain morphology of the deposition layer mainly consists of equiaxed crystals (∼300 μm) without an obvious preferred orientation. The deposition layer without direct heating by focused thermal energy could reduce the heat accumulation, resulting in a decrease in the temperature gradient and the morphology of equiaxed grains. The microstructure of a cylindrical sample was produced and has the same characteristics as with the deposition layer. The average microhardness of 172.63 HV, 167.95 HV and 169.26 HV are obtained in the top, middle and bottom regions, respectively. In addition, the tensile strengths are 500 MPa and 490 MPa, respectively.

Laser welding of GH3539 alloy for molten salt reactor: Processing optimization, microstructure and mechanical properties

GH3539 is a most promising material for next-generation molten salt reactors (MSR) due to its excellent performance in harsh high temperature molten salt environments. To promote the application of laser welding of GH3539 alloy in the molten salt reactor, the effect of various laser welding parameters on the weld geometry was investigated, as well as the microstructure and mechanical properties of GH3539 laser welded joints. The results indicate that GH3539 alloy has good laser weldability. The weld geometry of the laser welded alloy joint is significantly affected by the laser welding parameters. After processing optimization, the optimized laser welding process parameters were obtained. The microstructure close to the fusion line is a columnar crystal growing perpendicular to the direction of the fusion line. The core of the central portion of the welded joint consists of equiaxed crystals. No apparent “softened” heat-affected zone (HAZ) was discovered in the laser-welded joints. The hardness of the weld metal (WM) is approximately 130% of the hardness of the base metal (BM). Hardness values in different areas of the WM display unique distributions due to the influence of microstructure and intergranular carbides. A small amount of tiny solidification cracking, liquidation cracking is found in welded joints. Compared to specimens at room temperature (RT), both the tensile strength and elongation dropped significantly under the circumstances of elevated temperature. All fractures are located in the BM with a brittle fracture pattern.

In-situ investigation on tensile deformation and fracture behaviors of inhomogeneous microstructure during laser repair of Ti-6Al-4 V titanium alloy

Laser additive manufacturing, with its small heat-affected zone, high forming accuracy, and adjustable filler material, has great potential for use in the repair of aircraft engine blades. Nevertheless, it is inevitable to introduce a non-uniform microstructure during laser processing, which will cause a decrease in the components’ mechanical properties. To gain further insight into the mechanics of inhomogeneous structures under tensile load, digital image correlation (DIC) technology and in-situ tensile test are applied to study the mechanical response and fracture mechanism of inhomogeneous structures. It is indicated that the position of stress concentration changes in the β columnar during the tensile process, whereas the same remains constant in equiaxed crystals. The coordination deformation ability and mode of the RZ exhibit notable differences compared to that of the HAZ. The slips between the α phases in the β columnar lead to micro-cracks at the phase boundary and the propagation of Z-shaped cracks, while crack propagation along the grain boundary in the equiaxed crystal due to coordinated deformation by the different grains.

Stimulated corrosion damage of Ti-Al-N multilayer coatings under interval salt spray and hot condition

Engines for marine are subjected to synergistic chloride corrosion and hot oxidation. Here, we fabricated the Ti-Al-N multilayer coatings on TC4 substrate by multi-arc ion plating. The corrosion behavior of coating was conducted under the stimulated environment with 20 cycles of salt spray (35 ℃ for 22 h) and hot corrosion (500 ℃ for 2 h). Result showed that the vast majority of corrosive products were accumulated with increasing corrosion cycles, causing the substantial spallation and delamination of coating. However, the unique structures composing of TiAlN columnar crystals and TiN-Ti-TiN equiaxial crystals still benefited the excellent protective performance for coating.

Contribution of Si to the precipitation of γ'-phase in high Al content IN718 coatings and the phase transformation of α-Al2O3 during high temperature oxidation

The Al–Si composite-modified IN718 alloy has not been studied in depth thus far. In this paper, an Al–Si composite-modified IN718 coating was successfully fabricated by plasma cladding, and it was found that Al–Si increases the composition supercooling of the alloy melt, increases the proportion of equiaxed crystals in the coating, and greatly enhances the hardness of the coating through the precipitation of a large area of the γ'-phase. The changes in the properties of the γ and γ'-phases before and after Si doping were clarified by first-principles studies. High-temperature experiments show that the Al–Si IN718 coating has excellent resistance to high-temperature oxidation and that the addition of Si promotes the phase transformation of α-Al2O3 in the early stages of oxidation.

Effect of post-weld heat treatment on the microstructure and properties of titanium/304 stainless steel laser welding dissimilar metal joints with copper as the transition layer

Low elongation has been an important factor limiting the application of titanium/304 stainless steel (304SS) laser welding of dissimilar metal joint products. By adopting the post-weld heat treatment (PWHT) process of holding the welded joint at 400 ℃, 550 ℃ and 700 ℃ for 30 min, this study increases the elongation of the welded joint from 0.3 % to 2.21 % in the welded state and further analyses and investigates the structural changes in the organization and the formation process of intermetallic compounds (IMC) within the weld seam. The results showed that the acicular structure in the weld could not be eliminated by holding at 400 ℃ for 30 min, but only part of the residual stress was released, and the elongation was increased to 0.85 %. After holding at 550 ℃ for 30 min, a large number of equiaxed crystals appeared to replace the acicular structure in the weld and released the residual stress. With the enhancement of the IMC layer thickness, grain gap and deformation coordination ability, the elongation increased to 2.21 %. After holding at 700 ℃ for half an hour, the IMC layer becomes thinner, the grain gap decreases, the deformation coordination ability deteriorates, and the tensile strength and elongation decrease. In the tensile test, the fracture position was all at the weld. After being held at 400 ℃ for 30 min, the average tensile strength of the tensile sample increased from 330 MPa in the welded state to 352 MPa; after being held at 550 ℃ for 30 min, the average tensile strength of the tensile sample was 340 MPa, and the fracture elongation was 7.4 times that of the welded state, reaching 331 µm.

Migration Behavior of Inclusions at the Solidification Front in Oxide Metallurgy.

Distribution of inclusions plays an essential role in inducing intracrystalline ferrite, and the migration behavior of inclusions during solidification has a significant influence on their distribution. The solidification process of DH36 (ASTMA36) steel and the migration behavior of inclusions at the solidification front were observed in situ using high-temperature laser confocal microscopy. The annexation, rejection, and drift behavior of inclusions in the solid-liquid two-phase region were analyzed, providing a theoretical basis for regulating the distribution of inclusions. Analysis of inclusion trajectories showed that the velocity of inclusions decreases significantly as they near the solidification front. Further study of the force on inclusions at the solidification frontier shows three situations: attraction, repulsion, and no influence. Additionally, a pulsed magnetic field was applied during the solidification process. The original dendritic growth mode changed to that of equiaxed crystals. The compelling attraction distance for inclusion particles with a diameter of 6 μm at the solidification interface front increased from 46 μm to 89 μm, i.e., the effective length for the solidification front engulfing inclusions can be increased by controlling the flow of molten steel.

Electromagnetic levitation and solidification of ferrosilicon alloy and resulting microstructural evolution mechanisms

In this study, to improve pulverization of Fe–Si alloy, the evolution of its microstructure under container and containerless solidification conditions were investigated using electromagnetic levitation melting technology. The results indicated that the microstructure changed from dendritic crystals during container solidification to equiaxed crystals with containerless solidification. With an undercooling of 280K obtained by containerless solidification, the pulverizing sensitive elements (Al, P) disperse better in FeSi2 phase. The equiaxed Si grains with relatively uniform grain size obtained under ΔT=280K are distributed in random orientation. High angle grain boundaries are significantly more present with the increase of misorientation within FeSi2 grains. This texture is closely related to recrystallization in favor of grain refinement, which is attributed to the melt oscillation and dendrites remelting-recrystallization effects occurring in containerless solidification.

Electrical insulation improvement from interface regulation for high-temperature thin-film sensors on superalloy substrate

The stability and durability of insulation structure is crucial for the operation of thin-film sensors, especially at high temperature. However, it still faces great challenges in practical applications owing to the insulation failure during thermal cycles. In this study, an ALD Al2O3 film was introduced into the traditional TGO-sputtered Al2O3 insulation structure for interface regulation. After five thermal cycles up to 1000 °C, the modified insulation structure survived, while the control structure failed. The ALD Al2O3 layer could form denser equiaxed crystal during high-temperature crystallization, thereby preventing the propagation of cracks in sputtered Al2O3 due to volume shrinkage in phase transition. Furthermore, the ALD Al2O3 acted as a transition layer by forming semi-coherent interface with TGO Al2O3, stabilizing the multilayer insulation structure. Finally, Pt-PtRh thin-film thermocouples were fabricated on the modified insulation structure, which exhibited outstanding thermoelectric performance and stability at high temperature. Therefore, the interface regulation strategy proposed in this work could provide significant guidance for the development of high-temperature electrical insulation.

Study of thermal behavior and microstructure formation mechanism of CuCrZr alloy melted by laser powder bed fusion

The properties of CuCrZr alloy parts subjected to laser powder bed fusion (LPBF) are severely affected by the thermal behavior of the molten pool in relation to the solidified structure. Detailed understanding of the changes in the thermal behavior of the molten pool and the relationship between the thermal behavior and the solidified structure are required to achieve high-performance LPBF parts. In this study, a numerical simulation of temperature field changes was used to model the heat transfer and molten pool characteristics during the LPBF of CuCrZr alloys. The effect of linear energy density (LED) on the morphology and flow of the molten pool was studied using a finite element model (FEM), and the microstructure of the alloy was analyzed in combination with the temperature field. The results show that the shape of the molten pool obtained by the simulation is approximately circular, which differs from the typical comet-shaped molten pool for other alloys. The LED affects both the size of the molten pool and the flow of bubbles in the melt. When the LED is 800 J/m, the size of the molten pool is optimal, the bubbles in the melt can escape smoothly, and the highest relative density is achieved (98.23±1.4%). The simulation results are also in good agreement with the experimental data. The simulation obtained the difference in the temperature gradient along different directions as well. This anisotropy caused the solidified structure to form a large number of equiaxed crystals in the horizontal plane. At the same time, the circular shape of the molten pool caused a large deflection in the temperature gradient direction. The grain orientation of the horizontal plane formed an angle of 45° to the scanning direction. As a result of this larger temperature gradient in the vertical plane, a large number of columnar crystals are epitaxially grown.

Effects of ultrasonic vibration on microstructure and mechanical properties of 1Cr12Ni3MoVN alloy fabricated by directed energy deposition

Due to the rapid melting and solidification during directed energy deposition (DED) process, the defects and columnar crystals are likely to generate in the deposition layers, which reduce the quality and performance of the whole parts. Therefore, in order to improve the microstructure and mechanical properties of 1Cr12Ni3MoVN alloy manufactured by DED method, ultrasonic vibration (UV) has been employed to assist directed energy deposition process in this work. The results indicate that the high-intensity ultrasonic vibration can weaken the epitaxy growth tendency of crystal grains, and significantly improve plasticity while keeping an approximate strength. In addition, a two-dimensional numerical model is established to simulate the effect of ultrasonic vibration in the molten pool. The simulation results show that ultrasonic vibration remarkably improves the flow velocity and pressure in the molten pool, inducing the cavitation effect that breaks dendritic crystal and affects crystal characteristics. Meanwhile, the acoustic streaming effect changes the thermodynamic conditions and promotes high-temperature diffusion, which uniforms temperature distribution and reduces the temperature gradient in the molten pool. Thus the reduced temperature gradient G and raised solidification growth rate R promote the formation of fine equiaxed crystal characteristics after UV treatment. The product G × R increases and the ratio G/R decreases after UV treatment, resulting in the formation of fine equiaxed crystals.

Study on the effect of Ni60 transition coating on microstructure and mechanical properties of Fe/WC composite coating by laser cladding

Two coatings, i.e. a single Fe/WC cladding layer and a combination of a Fe/WC cladding layer and a Ni60 transition coating, were prepared on the surface of 60Si2Mn spring steel using the laser cladding technology. The effect of the Ni60 transition coating on the macromorphology, microstructure, element distribution, Vickers microhardness and tribological properties of the Fe/WC cladding layer was investigated. The experimental results show that the added Ni60 transition coating reduces the possibility of generating pores and cracks in the Fe/WC composite coating and promotes the upward elongation growth trend of columnar crystals, but has no significant effect on the solidification characteristics of the cladding layer. The solidification characteristics of both coatings consist of dendrites and interdendritic eutectics. In addition, the microstructure in the top and middle regions of the single Fe/WC composite coating mainly shows the distribution of snowflake-like equiaxed crystals, and columnar crystals dominate the bottom region. In terms of mechanical properties, the diffusion of the Ni element reduces the microhardness of the cladding layer and increases the average friction coefficient and wear volume of the Fe/WC composite coating, but these mechanical properties are still significantly enhanced compared with those of the matrix.

Nitriding Behaviour and Microstructure of High-Nitrogen Stainless Steel during Selective Laser Melting.

High-nitrogen stainless steels are widely used due to their excellent comprehensive performance. In this study, the effects of process parameters (laser power, scanning speed, and cavity pressure) on the formation of high-nitrogen stainless steels were studied by using conventional selective laser melting and high-pressure selective laser melting (HPSLM). The nitrogen content, nitrogen emission, phase composition, microstructure, and microhardness of the high-nitrogen stainless steel samples obtained through selective laser melting (SLM) were analysed by using an oxygen/nitrogen/hydrogen analyser, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction. The results showed that the maximum nitrogen emission in the SLM sample was 0.175 wt.%, the emission rate reached up to 54.7%, and the maximum nitrogen content in the HPSLM sample was 1.07 wt.%. There was no significant difference between the phase peak positions of the SLM samples with different laser powers and the original powder. The main phase of the HPSLM sample changed at 0.3 MPa (from α-Fe to γ-Fe phase); the microstructure of the SLM sample was mainly composed of columnar and cellular crystals, and columnar crystal bands formed along the direction of heat flow. The HPSLM sample was mainly composed of equiaxed crystals with a grain size of 10-15 μm. At an energy density of 136 J/mm3, the microhardness and relative density reached their peak values of 409 HV and 98.85%, respectively.

Study of Phase Evolution Behavior of Ti6Al4V/Inconel 718 by Pulsed Laser Melting Deposition

In this study, a pulsed laser was used as the heat source for the additive work. The Ti6Al4V/Inconel 718 alloy wire was deposited on the substrate by melting using a pulsed laser. Using the above method, single-layer and double-layer samples were printed. The sample material printed in this way is highly utilized. Compared to the complicated pre-preparation work of metal powder pre-mixing, this printing method is simple to prepare and only requires changing the wire feeding speed. The study of this paper provides a theoretical guide for the subsequent fusion deposition of heterogeneous wire materials. The samples were analyzed after molding using SEM, EDS and XRD to characterize the microstructure of the samples. The samples can be divided into three zones depending on the microstructure, the bottom columnar crystal zone, the middle mixed phase zone, and the bottom equiaxed crystal zone. From the bottom to the top of the sample, the phase microstructure changes as γ + Laves → α + β + Ti2Ni + TiNi + Ni3Ti → α + β. The hardness data show that the highest value in the transition zone is 951.4 HV. The hardness of the top part is second only to the transition zone due to a large number of equiaxed crystals. The bottom region is dominated by columnar crystals and is the softest of the three regions with the lowest hardness value of 701.4 HV.

Phase evolution and properties of AlxCoCrFeNi high-entropy alloys coatings by laser cladding

High-entropy alloys are class of structural materials that have excellent properties and are commonly used in laser additive manufacturing. In this paper, AlxCoCrFeNi (x = 0.5, 1.0, x is the molar ratio) high-entropy alloy coatings were prepared on the surface of H13 steel by using laser cladding technology. The effects of coatings on the phase composition, microstructure, element distribution, grain orientation, wear, and corrosion resistance of AlxCoCrFeNi ((x = 0.5, 1.0) coatings were analyzed. The results show that the Al0.5CoCrFeNi HEAc consists of FCC solid solution phase only, and the Al1.0CoCrFeNi coating consists of BCC/B2 solid solution phase. The microstructure changes from blocky crystals to equiaxial crystals. The average grain size decreased from 65.864 µm to 8.155 µm with the increase of Al content, and the high angle grain boundaries increased gradually with more uniform grain distribution. The average hardness values of AlxCoCrFeNi (x = 0.5, 1.0) coatings are 513.06 HV0.5 and 652.38 HV0.5, respectively. The friction coefficient and mass loss gradually decrease, and the wear form changes from abrasive wear to adhesive wear. AlxCoCrFeNi (x = 0.5, 1.0) HEAcs self-corrosion current density (Icorr) increases from 2.964 × 10−6 Acm−2 to 1.060 × 10−5 Acm−2, and the corrosion resistance gradually decreases.

Microstructure and mechanical properties of A7N01-T4 aluminum alloy metal inert gas welded joints filled with self-designed 7A48 aluminum alloy wire

7××× aluminum alloy is a metal with a high tendency to weld cracks. In the welding process, 7××× aluminum alloy wire was seldom used but low strength matching 4××× and 5××× aluminum alloy wire was used for joining, which had poor mechanical properties of welded joints. In this paper, a self-designed low copper 7A48 wire containing scandium was used as filler material for metal inert gas (MIG) welding of 4 mm thick A7N01-T4 aluminum alloy plates. The results show that the A7N01-T4 MIG welded joints were obtained with good seam formation and no crack formation. The equiaxed dendrites in the weld zone were found. The precipitated phases were primarily Mg-rich and Zn-rich, forming a typical 7××× aluminum alloy structure. In the fusion zone, fine equiaxial crystals were found, with a width of about 100 μm. In the heat-affected zone, grains growth occurred and the precipitated phase was dissolved or aggregated. The hardness of the WZ reached 81.7% of that of the base material and the softening of the WZ was not significant. The average tensile strength and elongation of the specimens were 364.9 MPa and 17.5%, respectively. The tensile fracture occurred in WZ and the fracture was dominated by microporous aggregation shear fractures with localized cleavage fractures occurring.

Research on high-temperature friction and wear performances of Stellite 12 laser cladding layer against coated boron steels

The stellite 12 layer was applied on H13 steel by laser cladding to increase the surface wear resistance at high-temperature. The tribological performance of stellite 12 laser cladding layer was compared with heat-treated H13 steel by pin-on-disc dry sliding tests against with Al–Si, GA (galvannealed), GI (galvanized) coated boron steels at 700 °C. The results indicated stellite 12 layer is composed of columnar, dendritic and equiaxed crystals along the section from substrate interface to the top surface without obvious cracks and other defects. Stellite 12 layer represents good wear resistance with the three kinds of coated boron steels, where the coefficients of friction (COFs) are lower than heat-treated H13 steel by 18.9%, 20.6% and 25.6% respectively, and wear rates are lower by 20%, 43% and 38% respectively. The wear mechanism of stellite 12 layer, i.e., a complex synergism involving oxidation, adhesion, diffusion, and plastic deformation, is mainly adhesive wear and oxidized wear. Compacting the oxide layer on the surface of stellite 12 pin is the key to reducing wear. In addition, the compacted oxide layer formed on the stellite 12 layer is mainly composed of oxides of Co, Cr, and transferred Al, Zn. Stellite 12 layer can improve the wear resistance of H13 steel, and friction and wear performances are affected by the compacted oxide layer. Compared with Al–Si coating, the stellite 12 cladding layer has a better antifriction effect on Zn-based steel sheet due to its thicker oxide layer. It has verified the development prospect of stellite 12 layer on reducing the surface wear at high-temperature.

Enhanced strength and ductility in a powder metallurgy Ti material by the oxygen scavenger of CaB6

• There exists a continuous oxide layer on the irregular HDH Ti powder surface. • CaB 6 addition promotes the improved sintered density and refines the grain size. • The scavenging of O by CaB 6 addition makes a high strength and superior ductility for α-Ti alloy. The challenge of producing a high-ductility titanium (Ti) material using inexpensive high-oxygen hydride-dehydride (HDH) Ti powder is hereby addressed by the incorporation of CaB 6 oxygen-scavenger. The oxygen-scavenging behaviour, microstructure evolution, mechanical behavior and improvement mechanism were systematically investigated. A continuous TiO 2 oxide layer with a thickness of approximately 9.3 nm is presented on the HDH Ti powder surface. The oxide layer will dissolve into Ti matrix during sintering, making the increase of c / a value and leading to the Ti-Ti bonds developing from plastic metal bonds toward brittle covalent bonds. The CaB 6 addition can scavenge O impurity and make a significant increase in tensile ductility for α-Ti matrix. A small addition of 0.2 wt.% CaB 6 provides a superior tensile elongation of 22.2% for Ti material, almost three times as high as that of pure Ti (7.5%). The increase of deformation twining activity and grain refinement are responsible for the improved ductility. Furthermore, the CaB 6 oxygen-scavenger can react with the surface oxide layer to in-situ form rod-like TiB and granular CaTiO 3 reinforcements, refining the coarse near equiaxed grain of α-Ti matrix into fine equiaxed crystals. The multiple mechanisms of grain-boundary strengthening, load-bearing strengthening of TiB and Orowan strengthening of CaTiO 3 nanoparticles work together to increase the tensile strength of Ti/CaB 6 composites. This work offers an effective method to fabricate high-performance Ti material using inexpensive high-oxygen HDH Ti powder.

Plasma-sprayed Ti-Si-C coatings and their crystallization behaviors depending on Ti powder content

For plasma sprayed ceramic coatings, their crystallization behaviors are significantly different from conventional crystal solidification due to the rapid solidification rate, which would affect their mechanical properties. At present, there are few studies on the crystallization behaviors of the sprayed ceramic coatings. In this work, the Ti-Si-C ceramic coatings were reactive-plasma-sprayed using Ti/Si/graphite agglomerated powders with different Ti powder contents. Their crystallization behaviors and microhardness were investigated. The results demonstrated that the Ti-Si-C coatings mainly composed of TiC/Ti5Si3/Ti3SiC2 phases. With the increase of Ti contents, the Ti3SiC2 and Ti5Si3 phases decreased first and then increased, while the TiC phases content showed an opposite trend. As the Ti content increased, the columnar crystals were gradually perpendicular to the surface. The inner part of the lamellae composed of equiaxed crystals and columnar crystals, and the crystalline morphology of the coating cross-sections all displayed a lamellar columnar structure. The maximum microhardness of the coatings (HV 1201 ± 100) was obtained at a Ti/Si/graphite ratio of 3:1:2.