Influence of spark plasma sintering on microstructure and wear behaviour of Ti-6Al-4V reinforced with nanosized TiN

Ti-6Al-4V/TiN composites were successfully consolidated by spark plasma sintering (SPS). TiN addition to Ti-6Al-4V was varied from 1% to 5% (volume fraction). The effect of TiN addition on the densification, microstructure, microhardness and wear behaviour of Ti-6Al-4V was studied. Experimental results showed reduction in sintered density of the compacts from 99% to 97% with increase in TiN content. However, an increase in microhardness value was recorded from HV_0.1 389 to HV_0.1 488. X-ray diffraction (XRD) analysis showed that the intensity of diffraction peaks of TiN phase in the composites increased also with formation of small amount of secondary Ti₂N phase. SEM analysis of SPS sintered nanocomposites possessed a refinement of α/β phase microstructure in Ti-6Al-4V with the presence of uniformly dispersed TiN particles. The worn surface of the composite showed improved abrasive wear resistance with non-continuous grooves as compared to the sintered Ti-6Al-4V without TiN addition.     

Effect of Ball Milling of Feedstock Powder on Microstructure and Properties of TiN Particle-Reinforced Al Alloy-Based Composites Fabricated by Cold Spraying

Dense Al5356/TiN composites with TiN particles uniformly dispersed in the matrix were produced by cold spraying (CS) using both the mechanically mixed (MM) and ball-milled (BM) powder blends with 50 wt.% TiN compared to that of CS pure Al5356 deposit. The microhardness of the composite deposited with the BM blend was three times higher than that of pure Al5356 coating. Compared to the coating deposited with the MM powder (MM composite), the hardness of the coating deposited with the BM powder (BM composite) was significantly increased owing to the increase of TiN volume fraction, which is comparable to that of the MM composite deposited with the 75 wt.% TiN feedstock. The adhesive strength of the composites was remarkably improved in comparison with the pure Al5356 coating because of the pinning effect of TiN particles. The coefficient of frication (COF) and wear rate (WR) were measured using a ball-on-disc tribometer. It was found that the COFs and WRs of the composites were much lower than those of pure Al5356 coating. Especially, the WRs of the MM and BM composites were, respectively, decreased by about 14 and 50 times than that of pure Al5356 deposit. This phenomenon could be ascribed that TiN particles contribute to a third-body abrasion in the following sliding process, which benefits the decrease of COF by rolling action partially instead of sliding action. For the BM composite, more and finer TiN particles present in the worn surface compared to the MM composite, which will be helpful to the further decrease of the COF and WR.     

Fabrication and tribological properties of titanium nitride coatings incorporating solid lubricant microreservoirs

The concept of incorporating microscopic reservoirs within a hard coating for the purpose of solid lubricant storage and supply during wear of interacting surfaces has been investigated in this study. A novel method was devised using ceramic beads (1.5-10 μm diameter) as placeholders during the deposition of a TiN coating by reactive sputter deposition. A pin-on-disk wear test was used to test these coatings using graphite and sputter-deposited carbon as the solid lubricant, and an alumina counterface. When tested without any lubricant, the presence of the microreservoirs in the TiN coating appeared to degrade the mechanical integrity of the coating leading to rapid failure. With the graphite lubricant present, the frictional behavior ranged from levels similar to the TiN coating alone, to that of graphite alone. Tests of the TiN coating made using 10 μm beads running against an aluminum counterface showed substantial improvement when the microreservoirs were present. Optical microscopy examination of the wear tracks showed the microreservoirs were generally successful at trapping the graphite lubricant during wear. With a sufficient density and appropriate distribution of the microreservoirs significant improvements in tribological performance can be realized.     

Comparative wear performance of titanium based coatings for automotive applications using exhaust gas recirculation

This paper reports tribological characterization of titanium based coatings ion bonded on steel balls for automotive applications using exhaust gas recirculation (EGR). It is well known that lubricating oil drawn from EGR operated engine is contaminated with soot and higher amounts of wear debris compared to non-EGR operated engine. In this study, steel balls coated with TiN, TiAlN and TiCN are investigated in both fresh lubricating oil and EGR stressed oil for a comparative assessment of their wear characteristics in two mediums. Normal load was applied on the samples, tested against a rotating cast iron disk, simulating ring-liner interaction. In each experiment, about one quarter of disk was dipped in the oil (a) to ensure the presence of a thin oil film on the disk-ball interface during the experiment, and (b) to avoid exposure of the worn surface to atmospheric air. The results reveal that the wear rates of the coatings based on the change in the scar diameters of the samples, tested in EGR oil was 2-4 times higher than that of fresh lubricating oil. It was found that despite lowest hardness, TiN coated samples showed smaller scar diameters than TiAlN and TiCN coated samples in both lubricating oil environments. A simple geometric model was used to calculate the thickness of the coating removed as a function of the test duration. Results show that TiN coatings last for 120 min in fresh oil as compared to 30 min in the EGR oil under normal loading, whereas TiAlN and TiCN coating last for 60 and 30 min respectively in fresh oil and wear out in 15 min in EGR oil.     

Microstructural characterization and mechanical behaviours of TiN-graphite composites fabricated by spark plasma sintering

The effects of milling time on the particle size distribution (PSD), densification, microstructure, hardness and fracture toughness of spark plasma sintered (SPS) TiN+graphite ceramic were studied. TiN with varying amount of graphite (1, 3, and 5 wt%) were milled at different milling time (8, 24 and 40 h), thereafter sintered at sintering temperature of 1800 °C, holding time of 10 min and pressure of 50 MPa. The relative density and hardness increased as milling time progressed from 24 to 40 h, however, the relative density, hardness, and particle size decreased after 8 h of milling. The microstructural analyses showed that a fully sintered TiN+graphite compact could be achieved at sintering temperature of 1800 °C, with no significant grain growth. Residual stress effect of TiN+5 wt% graphite composite was analyzed using XRD method and the result indicated that there is no significant residual stress on the sample. The relative density, Vickers hardness and fracture toughness of TiN+ 1 wt% Gr, milled for 40 h were 99.24%, 13.90 GPa and 4.0 MPa.m^1/2 respectively.     

The influence of boron content on the tribological performance of Ti-N-B coatings prepared by thermal CVD

In this work, Ti-N-B coatings have been deposited by thermal chemical vapor deposition (CVD). The effect of boron varying between 0 and 35.1 at.% on coating structure, mechanical and tribological properties was investigated. The coatings reveal a dual-phase structure of TiN and TiB₂ above 1 at.% B. The addition of boron causes grain refinement and changes the structure from columnar for TiN to fine-crystalline. Coating hardness increases continuously from 20 GPa for TiN to 45 GPa at 35.1 at.% B. Ball-on-disc tests against alumina were conducted at 25, 500 and 600 °C. At 25 °C the friction coefficients increase from 0.75 for TiN to about 1.0 for boron contents up to 13.1 at.%, while values down to 0.26 were measured at 35.1 at.% B. The friction coefficients at 500 and 600 °C increase from 0.55 for TiN to 0.8-1.0 for the highest boron content. At 25 °C the lowest wear rates were obtained for the highest boron contents, while the opposite behavior was found for 500 and 600 °C. Extensive coating oxidation resulted in the highest wear rate at 500 °C for 35.1 at.% B, but the wear resistance improved at 600 °C. Raman spectroscopy of the oxide layer revealed the preferred formation of anatase at the expense of rutile for high boron concentrations.     

Comparative studies on corrosion and tribological performance of multilayer hard coatings grown on WC-Co hardmetals

Multilayer TiN/TiCN/TiCN/TiC/TiN and TiN/TiCN/TiCN/TiC/Al₂O₃ hard coatings with total thicknesses of 15.7 μm and 9.3 μm were deposited on WC-10Co substrates using a chemical vapor deposition system. Evaluation of surface, cross-section morphologies, chemical composition and phases of coatings were analyzed by field emission scanning electron microscopy (FESEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) analyses respectively. Corrosion properties were evaluated in 3.5 wt% NaCl medium using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Tribological properties of fabricated multilayer hard coatings were evaluated using pin-on-disk tests. Results show that active dissolution of the WC-10Co occurred while the coated samples showed more anodic slopes as well as lower corrosion current densities. The corrosion current densities of 3.3 × 10⁻⁷ A/cm² and 7.5 × 10⁻⁸ A/cm² were obtained for the TiN/TiCN/TiCN/TiC/TiN and TiN/TiCN/TiCN/TiC/Al₂O₃ coated specimens which are much lower than 4 × 10⁻⁶ A/cm² of substrate. EIS analysis confirmed the results of potentiodynamic polarization curves. Delamination of the TiN coating and formation of titanium oxide compounds on the surface of the TiN/TiCN/TiCN/TiC/TiN coating revealed that oxidative wear mechanism is dominant for this sample, while adhesive wear mechanism was dominant for the TiN/TiCN/TiCN/TiC/Al₂O₃ coated sample.     

Formation of Al-TiN metal matrix composite via mechanochemical route

Aluminum metal matrix composites (MMC) dispersed with particulate titanium nitride have been prepared by ball milling of elemental powders Al and Ti with ring-type organic compound pyrazine in benzene solution. A one-step formation process could not form the desired Al-TiN MMC. The composite was obtainable only by a subsequent thermal treatment. For two-step processing, the TiN formed in the early stage of milling could then be dispersed in the Al matrix homogeneously and Al-TiN composite could be successfully synthesized. The crystalline size of TiN was found to be 9 nm.     

Enhanced thermal stability and wear resistance of TiCN-SiC-TiN-Cr3C2-Co cermet modified by B4C for cutting tool application

In this work, a suitable cermet compositions based on TiCN-SiC-TiN-Cr₃C₂-Co-B₄C is identified for cutting tool purpose. The cermets were sintered using spark plasma sintering with the addition of different weight percentages of B₄C (5%, 10%, 15%) in TiCN - SiC - TiN - Cr₃C₂ - Co cermets. The cermets were subjected to the annealing process at three different temperatures of 600 °C, 800 °C, and 1000 °C for a constant soaking time of 4 h to study their thermal stability. All the cermets' compositions showed good thermal stability up to 800 °C and 55% TiCN – 15% SiC – 5% TiN – 5% Cr₃C₂–10% Co – 10% B₄C cermets showed better thermal stability up to 1000 °C. There was a change in microstructure and formation of the oxide phases in the cermets during the high temperature (1000 °C) annealing process and overall lead to a decrease in hardness. The sintered cermets were also subjected to sliding wear in the pin on disk apparatus. EN31 steel disk was used as a counter disk. The wear testing was done at different loads (20 N, 25 N, 30 N, 35 N) and at different sliding velocity (0.55 m/s, 1 m/s, 1.5 m/s, 2 m/s) with a constant track distance of 1000 m. Wear rate was at its highest value of 9.74 × 10⁻⁷ mm³/Nm for the cermet 65% TiCN - 15% SiC - 5% TiN - 5% Cr₃C₂₋10% Co and the lowest wear rate noted was 1.18 × 10⁻⁷ mm³/Nm for cermet 55% TiCN - 15% SiC - 5% TiN - 5% Cr₃C₂₋10% Co – 10% B₄C and the B₄C addition has improved the wear resistance of the cermets.     

High thickness Ti/TiN multilayer thin coatings for wear resistant applications

Hard coatings like titanium nitride (TiN) normally contain a high degree of internal stress (usually compressive in-plane parallel with the surface) owing to growth defects developed during the deposition process and thermal mismatch effects after final cooling; it is, therefore, difficult to produce single-layer TiN coatings thicker than 6-7 μm, without adhesion problems. In the present study, thick coatings (i.e. > 10 μm) have been achieved by alternate multilayering of TiN with Ti interlayers, leading to a tougher and less-stressed film. However, having a constant distribution of titanium interlayer thickness is not necessarily the best solution to achieve maximum performance in terms of wear resistance and hardness. The residual stress distribution along the thickness is unlikely to be constant with the inner layers being more stressed due to a greater amount of thermal differential strain. Following this guideline, a series of numerical simulations was performed in order to calculate the residual stress through thickness distribution due to the deposition process. Three sets of multilayered Ti/TiN coatings having both constant and variable Ti interlayer thickness were modelled and deposited, using a reactive arc PVD process. Mechanical and tribological properties were characterized using static and depth sensing Vickers micro-hardness indentation tests, rotating wheel (dimpling grinder) abrasive wear tests and Rockwell C adhesion tests. Coating interface characterizations were made by SEM-EDS. Results showed that adhesion can be significantly improved by adopting a titanium through thickness quantity increasing towards the interface: an optimized distribution allows also higher hardness and wear resistance to be obtained, as it requires a lower total amount of titanium to obtain good adhesion properties.     

Temperature dependence of microstructure evolution during hot pressing of ZrB2–30 vol.% SiC composites

Microstructure evolutions of ZrB₂–30 vol.% SiC composites, prepared by hot pressing at different processing temperatures (1700, 1850 and 2000 °C) for 30 min under 10 MPa, were investigated by optical microscopy, scanning electron microscopy and transmission electron microscopy (TEM). The microstructures of the fabricated composites were compared with and the effects of the processing temperature on the sintering process and densification behavior during the hot pressing were found. The amount and the orientation of dislocations which were indicated by TEM analysis in the sample hot pressed at 1700 °C showed that no plastic deformation and atomic diffusion occurred. But the presence of amorphous phases and rearrangement of particles are signs of the fact that liquid phase sintering and particle fragmentation/rearrangement is the main densification mechanism. On the other hand, in the sample hot pressed at 1850 °C, aggregation of dislocations behind the grain boundaries and the presence of twinnings addressed wide plastic deformations which were introduced as the main densification mechanism at 1850 °C. Finally in the sample hot pressed at 2000 °C, lower amounts of un-oriented dislocations and also some annealing twinnings were observed in TEM micrographs together with fractographical SEM analysis and showed that the atomic diffusion is the dominant densification mechanism of hot pressed ZrB₂–30 vol.% SiC composite.     

Friction and wear properties of TiN,TiAlN, AlTiN and CrAlN PVD nitride coatings

Four nitride coatings, TiN, TiAlN, AlTiN and CrAlN were deposited on YG6 (WC + 6 wt.% Co) cemented carbide by cathodic arc-evaporation technique. The friction and wear properties were investigated and compared using ball-on-disc method at high speed with SiC ball as a counter material. The tests were evaluated by scanning electron microscopy, X-ray diffractometer, energy dispersive X-ray, micro hardness tester and an optical profilometer. The results showed that TiN and TiAlN coatings presented lower friction coefficient and lower wear rate, and that high Al content AlTiN and CrAlN coatings didn't present better anti-wear properties in this test. Oxidation and abrasive wear were the main wear mechanism of TiN coating. In spite of the observation of micro-grooves and partial fractures, TiAlN possessed perfect tribological properties compared with the other coatings. High Al content increased the chemical reactivity and aroused severe adhesive wear of AlTiN coating. CrAlN coating presented better properties of anti-spalling and anti-adhesion, but abundant accumulated debris accelerated wear of the coating under this enclosed wear environment.     

Surface characterization and mechanical property of TiN/Ti-coated NiTi alloy by PIIID

A hard and adherent TiN/Ti thin film of approximately 3 μm in thickness was deposited on the surface of Ti-50.6 at.% Ni alloy by the PIIID technique. The surface composition and chemical state of the coated samples were evaluated by XPS. The XPS results indicate that titanium oxide and titanium oxynitride were present on the TiN surface. The spectra of Ti 2p, N 1s, O 1s and C 1s electrons before and after the film being sputter etched were also discussed. Scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS) analyses demonstrate that an interfacial layer, containing Ti, N and Ni, was formed at the interface between the TiN and Ti coatings. Sliding wear tests show that the TiN coating significantly reduces the friction coefficient and improves wear resistance of the NiTi alloy.     

N2流量对等离子体增强磁控溅射TiN涂层的影响

目的研究N_2流量对等离子体增强磁控溅射TiN涂层组织结构和性能的影响,优化TiN涂层的制备工艺。方法在不同N_2流量的条件下,采用等离子体增强磁控溅射法制备TiN涂层。采用3D形貌仪和扫描电子显微镜观察涂层的表面形貌,利用X射线衍射仪测定涂层的相结构,利用显微硬度计测试涂层试样的硬度,利用球-盘摩擦磨损试验机考察涂层试样的摩擦磨损性能,利用能谱仪分析磨痕表面的化学组成。结果 N_2流量小于61.5 mL/min时,增加N_2流量对总气压和靶电压的影响很小;N_2流量超过61.5 mL/min后,总气压和靶电压均随着N_2流量的增加而显著增大。随着N_2流量的增大,制备的TiN涂层X射线衍射谱中的TiN(111)、TiN(220)衍射峰强度不断增大,TiN(200)衍射峰强度先不变后突然减小。N_2流量约为61.5 mL/min时,制备的TiN涂层试样的致密性最好,硬度最高。N_2流量在50~61.5 mL/min范围内,制备的TiN涂层试样的磨损率较低,最低可达7.4×10~(-16) m~3/(N·m)。当N_2流量超过63 mL/min后,TiN涂层试样的磨损率显著增大。结论 N_2流量对等离子体增强磁控溅射TiN涂层择优取向、硬度及摩擦磨损性能的影响较显著,N_2流量约为61.5 mL/min时,制备的TiN涂层试样的硬度和耐磨性最好。     

Improved properties of Ti-Al-N coating by multilayer structure

Multinary Ti-Al-N coatings are used for various applications where hard, wear and oxidation resistant materials are needed. Here, we prepare TiAlN/TiN nano-multilayer coatings with modulation period of ~ 20 nm in order to further improve the properties of Ti-Al-N coating. Annealing of both coatings up to 700 °C results in an increase in hardness due to the precipitation of cubic Al-rich domains by spinodal decomposition. Multilayer structure results in an increase in adhesion with substrates from ~ 72 N for Ti-Al-N single layer coating to 98 N for TiAlN/TiN nano-multilayer coating. Additionally, the interfaces of TiAlN/TiN nano-multilayer coating retard the outward diffusion of metal atoms (Al and Ti) and inward diffusion of O while exposing coatings in air atmosphere with elevated temperature, and thus improve its oxidation resistance. An improved machining performance regardless of continuous cutting and milling is obtained by TiAlN/TiN nano-multilayer coated inserts, which can be attributed to the combined effects of higher adhesion with substrates and better oxidation resistance.     

Tribological behavior of a TiSiCN coating tested in air and coolant

One TiSiCN coating and one TiN coating as a comparison basis were investigated in this paper. The coatings were deposited on stainless steel substrates using a Plasma Enhanced Magnetron Sputtering (PEMS) process, a variation of the physical vapour deposition (PVD) technique. The XRD pattern for the TiSiCN coating implied that the coating either consists of TiN and TiC phases or C be incorporated in TiN as a single solid solution. Both coatings exhibited good adhesion, although their thickness (17 μm-45 μm) was much larger than that of many commercial PVD coatings. The TiSiCN coating showed higher hardness than the TiN coating. The sliding tribological behavior of the coatings against alumimium and alumina counterparts was studied both in air and in a coolant (Hangsterfer's S-500) by pin-on-disc tests. Scanning electron microscopy (SEM) was used to examine the wear tracks on the discs and the wear scars on the pins. Compared to the TiN coating, the TiSiCN coating exhibited lower wear rates and lower coefficients of friction (C.O.F.) against those two kinds of counterparts when tested in air. The cutting coolant provided a lubricant effect and reduced the adhesive wear and C.O.F. between the coating and the counterpart.     

Densification,microstructure and tribomechanical properties of SPS processed β-SiAlON bonded WC composites

Densification, microstructure and tribomechanical properties of spark plasma sintering (SPS) processed β-SiAlON (20–40 wt%) bonded WC matrix composites have been reported. All the specimens achieved almost their theoretical density values after SPS at 1750 °C for 25 min under 40 MPa. Incorporation of β-SiAlON in WC significantly altered the densification trend of the composites resembling that of pure β-SiAlON. Microstructural investigations using scanning and transmission electron microscopy revealed formation of principally equiaxed, micron sized WC grains surrounded by the sub-micron to micron sized β-SiAlON phase. The interface region between WC and β-SiAlON was found to be free of any reaction product. Energy dispersive X-ray spectrum confirmed presence of characteristics elements in both WC and β-SiAlON phases in the composite. The maximum Vickers hardness (~18 GPa) and fracture toughness (~6.8 MPa-m^0.5) under 10 kgf were obtained for the 30 wt% β-SiAlON/WC composite. These were almost 6% and 50% higher, respectively, than those obtained for pure WC. Indentation size effect (ISE) analyses of some selected specimens indicated moderate sensitivity towards ISE (Meyer's exponent = 1.802) of the 30 wt% β-SiAlON/WC composite and higher true hardness (~15.4 GPa) than those obtained for both the constituent phases. The load dependence of fracture toughness of some selected specimens has also been reported. Unlubricated wear studies under 30 N up to 250 m using ball-on-disc configuration indicated ~46–55 times higher specific wear rate of the β-Si₃N₄ ball when rubbed against the composites compared to that (~8 × 10⁻⁶ mm³/N-m) obtained against pure WC. Formation of compacted flaky tribo-layer within the wear track of the composites was evidenced.     

Micro-abrasive wear of DC and pulsed DC titanium nitride thin films with different levels of film residual stresses

In this work, six specimens with titanium nitride (TiN) thin films and cemented carbide (WC-Co) substrates were analyzed in terms of their micro-abrasive wear behavior. These specimens were obtained from a previous work, in which film depositions were conducted varying parameters such as bias (0, − 50 or − 100 V), type of target power (DC or pulsed DC) and, in the cases where substrate bias was zero, substrate condition (ground or floating). As a result, the level of film residual stresses varied from specimen to specimen, in the range from 4 to 11 GPa (compressive). In this work, micro-abrasive tests were run on these six specimens, using balls of AISI 1010 steel and an abrasive slurry with distilled water and silicon carbide particles with average particle size of 5 μm. Results were analyzed in terms of the wear mechanisms observed at the worn surface and also in terms of the wear resistance, characterized by the wear coefficient (k). Trends indicate a decrease in film wear rate with an increase in the value of film residual compressive stresses, as long as the adhesion was not impaired. Different values of film wear coefficient (k_c) were calculated for specimens obtained with ground and floating voltage substrates, although similar values of film residual stresses were measured in both cases.     

Microwave-assisted solid-state decomposition of La[Co(CN)6]·5H2O precursor: A simple and fast route for the synthesis of single-phase perovskite-type LaCoO3 nanoparticles

Pure and single-phase nanoparticles of perovskite-type LaCoO₃ were prepared via microwave-assisted solid-state decomposition of La[Co(CN)₆]·5H₂O precursor in the presence of CuO powder as a strong microwave absorber within a very short reaction time of 10 min. Product was characterized by X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR), Raman spectroscopy, UV–visible spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and surface area measurement. The method is simple, fast and energy efficient and resulted in fine particles (10–30 nm) with high specific surface area and narrow size distribution. This hybrid microwave heating route is promising for the synthesis of other mixed oxide and related compounds.     

Effect of Ni addition on the densification of TiC: A comparative study of conventional and microwave sintering

This study deals with the effect of conventional sintering and microwave sintering on the densification kinetics of Titanium Carbide (TiC) in the presence of Ni (1, 1.5, 2 wt%). TiC compacts were obtained after uniaxial pressing of powders synthesised by ball milling of Titanium and Carbon and sintering was done in the presence of Nickel. The samples prepared were subjected to conventional as well as microwave sintering. The XRD and SEM analysis were used for a study of the reaction of Ti and C powders upon addition of Ni, which reduced the sintering temperature to 1200 °C. The densification of TiC powders was due to the Ti-Ni eutectic system, the liquid phase formed at this temperature assisting the sintering process. The SEM images revealed the flake like structure of TiC in which the carbon diffused into Ti upon the addition of Ni, thereby supporting enhanced mass transfer. The XRD pattern showed the presence of Titanium Oxide (TiO₂) along with TiC which resulted in non-uniform distribution of hardness. Maximum hardness was achieved in the conventional sintered compacts which gradually increased with increase in Ni addition. The presence of the oxide phase and the formation of micro cracks resulted in non-uniform hardness for microwave sintered compacts. The maximum hardness of conventional sintered compact (375 HLD) was nearly 1.5 times more than the maximum hardness of the microwave sintered compact (250 HLD). The density of the microwave sintered compact was found to be higher by 8% than with the conventionally sintered compact.