Strengthening and toughening of TiN-based and TiB2-based ceramic tool materials with HfC additive

Effects of HfC addition on the microstructures and mechanical properties of TiN-based and TiB₂-based ceramic tool materials have been investigated. Their pore number decreased gradually and relative densities increased progressively when the HfC content increased from 15 wt% to 25 wt%. The achieved high relative densities to some extent derived from the high sintering pressure and the metal phases. HfC grains of about 1 µm evenly dispersed in these materials. Both TiN and TiB₂ grains become smaller with increasing HfC content from 15 wt% to 25 wt%, which indicated that HfC additive can inhibit TiN grain and TiB₂ grain growth, leading to the formation of a fine microstructure advantageous to improve flexural strength. Especially, TiB₂-HfC ceramics exhibited the typical core-rim structure that can enhance flexural strength and fracture toughness. The toughening mechanisms of TiB₂-HfC ceramics mainly included the pullout of HfC grain, crack deflection, crack bridging, transgranular fracture and the core-rim structure, while the toughening mechanisms of TiN-HfC ceramics mainly included pullout of HfC grain, fine grain, crack deflection and crack bridging. Besides, HfC hardness had an important influence on the hardness of these materials. Higher HfC content increased Vickers hardness of TiN-HfC composite, but lowered Vickers hardness of TiB₂-HfC composite, being HfC hardness higher than for TiN while HfC hardness is lower than for TiB₂. The decrease of fracture toughness of TiN-HfC ceramic tool materials with the increase of HfC content was attributed to the formation of a weaker interface strength.     

Comparative study on wear behavior of plasma sprayed Al2O3 coatings sliding against different counterparts

Although the friction and wear behavior of plasma sprayed aluminum matrix ceramic coatings have been extensively discussed in the last decades, only few researches have been carried out the wear mechanisms sliding against different pairs. The tribological behaviors of plasma sprayed Al₂O₃ coating sliding against ZrO₂, Si₃N₄, Al₂O₃ and stainless steel balls in air were comparatively investigated in this study. It was showed that Al₂O₃ coating sliding against different counterparts exhibited diverse tribological behaviors, which could be mainly ascribed to the different mechanical properties of counterparts. Meanwhile, the tribochemical reactions influenced the friction performances significantly. Moreover, the transform of γ-Al₂O₃ to α-Al₂O₃ occurred during the friction, which was closely related to the coefficient of friction and thermal conductivities of counterparts. The main wear of Al₂O₃ coating sliding against ceramic materials resulted from the brittle fracture and abrasive wear. While it was dominated by adhesive wear when sliding against stainless steel, and accompanied with abrasive wear.     

Comparison of dry sliding wear behavior of plasma sprayed FeCr slag coating with Cr2O3 and Al2O3-13TiO2 coatings

The microstructure and dry sliding wear performance of thermally sprayed FeCr slag coating were evaluated in comparison with those of commercially available Al₂O₃-13TiO₂ and Cr₂O₃ ceramic coating powders to assess the applicability of FeCr slag (FS) powder, fabricated from industrial waste, as a ceramic top-coating material against wear. Ceramic top coats and underlying NiCoCrAlY bond coats were deposited on AISI 316L samples via atmospheric plasma spraying (APS), and their tribological properties were assessed using a ball-on-disc test rig at room temperature. As a result, FS coating exhibited the lowest worn volume, although it has the lowest surface hardness. Tribolayer formation was observed on the surface of the samples which were subjected to dry sliding wear tests. Delamination type wear is the dominant wear mechanism for Cr₂O₃ and FS coatings, whereas local spallation areas arising from plastic deformation were observed on the surface of Al₂O₃-13TiO₂ coatings. The results suggested the applicability of FS powder as a candidate ceramic top coating material against wear.     

Wear behavior of Fe3Al-TiN-TiB2 HVOF coatings: A comparative study between in situ and ex situ powder processing routes

In the present study, the tribological properties of High Velocity Oxy-Fuel (HVOF) coatings prepared from Fe₃Al-based composite powders were investigated. The iron aluminide matrix of the composite powders was reinforced with TiN and TiB₂ particles made using two different processing routes: a) an in situ method where fine ceramic particles were formed in the matrix by the reaction between Ti and BN, and b) an ex situ method where preformed coarse TiN and TiB₂ particles were added to the matrix. The tribomechanical performance of the coatings was assessed using indentations and pin-on-disc wear tests. Compared to ex situ samples, the Fe₃Al-based coatings strengthened with in situ ceramic particles exhibit higher microhardness and wear resistance regardless of the sliding velocity. The presence of voids, cracks and scratches/grooves in the wear track of the in situ coatings and the coating material transferred to the corresponding counterpart suggest that coatings with fine reinforcing particles fail predominantly via delamination and adhesive wear mechanisms. In the case of the ex situ coatings, the presence of a significant amount of hard ceramic particles within the wear track indicates that abrasive wear plays a dominant role in the degradation mechanism. Oxidation wear also contributed to material removal at high sliding velocity since transfer materials inside the wear track contain a high oxygen content compared to the unworn region regardless of the coating type.     

Wear mechanisms of TiN–TiB2 ceramic in sliding against alumina from room temperature to 700 °C

TiN–TiB₂ ceramic was prepared by the reactive hot-pressing method using titanium and BN powders as raw materials. The friction and wear properties of TiN–TiB₂ ceramic were evaluated in sliding against alumina ball from room temperature to 700 °C in air. The TiN–TiB₂ ceramic has a relative density of 98.6%, a flexural strength of 731.9 MPa and a fracture toughness of 8.5 MPa m^1/2 at room temperature. The TiN–TiB₂ ceramic exhibits a distinct decrease in friction coefficient at 700 °C as contrasted with the friction data obtained at room temperature and 400 °C. Wear mechanisms of TiN–TiB₂ ceramic depend mainly upon testing temperature at identical applied loads. Lubricious oxidized products caused by thermal oxidation provide excellent lubrication effects and greatly reduce the friction coefficient of TiN–TiB₂ ceramic at 700 °C. However, abrasive wear and tribo-oxidation are the dominant wear mechanisms of TiN–TiB₂ ceramic at 400 °C. Mechanical polishing effect and removal of micro-fractured grains play important roles during room-temperature wear tests.     

Tribological properties of SiC-B4C ceramics under dry sliding condition

SiC-B₄C ceramic composites with different ratios of SiC to B₄C were produced. The relative density, mechanical properties, initial surface characteristics, dry sliding tribological properties against SiC ball and worn surface characteristics of the SiC-B₄C ceramics were studied. Results of dry sliding tribological tests showed that, 40 wt. % SiC-60 wt. % B₄C ceramic composite had the best tribological properties in SiC-B₄C ceramic composites. A relief structure with height difference of 10−30 nm between B₄C grains and SiC grains is formed after dry sliding. This relief structure, on the one hand, can reduce real contact area on interface, decreasing adhesion effect, and on the other hand, can fix or trap the wear pieces formed on sliding interface during the dry sliding process, reducing the abrasive wear. However, there is a limit to the beneficial influence of decreased adhesion effect and reduced abrasive wear, and an optimum proportion of relief structure. Pores can also fix or trap some wear pieces, reducing the abrasive wear. Under the condition of strong bonding between SiC grains and B₄C grains, the SiC-B₄C ceramic composites with higher porosity can obtain better tribological properties. In addition, it is observed by AFM that the depth of scratch on B₄C grains is shallower than that on SiC grains. Hence, it is demonstrated by micro scale measurement that the wear rate of B₄C is lower than that of SiC in this study.     

Effect of MoS2/PTFE coatings on performance of Si3N4/TiC ceramics in dry sliding against WC/Co

To enhance the tribological performance of Si₃N₄/TiC ceramics, MoS₂/PTFE composite coatings were deposited on the ceramic substrate through spraying method. The micrographs and basic properties of the MoS₂/PTFE coated samples were investigated. Dry sliding friction experiments against WC/Co ball were performed with the coated ceramics and traditional ones. These results showed that the composite coatings could significantly reduce the friction coefficient of ceramics, and protect the substrate from adhesion wear. The primary tribological mechanisms of the coated ceramics were abrasive wear, coating spalling and delamination, and the tribological property was transited from slight wear to serious wear with the increase of load because of the lower surface hardness and shear strength. The possible mechanisms for the effects of MoS₂/PTFE composite coatings on the friction performance of ceramics were discussed.     

Self-lubricating behaviors of Al2O3/TiB2 ceramic tools in dry high-speed machining of hardened steel

In this paper, Al₂O₃/TiB₂ ceramic cutting tools with different TiB₂ content were produced by hot pressing. The fundamental properties of these ceramic cutting tools were examined. Dry high-speed machining tests were carried out on hardened steel. The tool wear, the cutting temperature, the cutting forces, and the friction coefficient between the tool and the chip were measured. It was shown that both the wear rates and the friction coefficient at the tool–chip interface of Al₂O₃/TiB₂ ceramic cutting tools in dry high-speed machining of hardened steel were reduced compared with that of in low-speed machining. The mechanisms responsible were determined to be the formation of a self-lubricating oxide film on the tool–chip interface owing to the tribological–chemical reaction by the elevated cutting temperature. The composition of the self-lubricating film was found to be the oxidation product of TiB₂ grains, which serves as lubricating additive on the wear track of the tool rake face. The appearance of this self-lubricating oxide film contributed to the improvement in wear resistance and the decrease of the friction coefficient. This action was even more effective with higher TiB₂ content. Cutting speed was found to have a profound effect on the self-lubricating behavior. In dry low-speed machining of hardened steel, the Al₂O₃/TiB₂ tools showed mainly adhesive and abrasive wear. While in dry high-speed machining, oxidation wear of the ceramic tools was the dominant mechanism due to the very high cutting temperature. No oxide film was formed on the tool–chip interface while machining in nitrogen atmosphere, and the tool wear resistance was correspondingly decreased.     

Wear properties and microstructures of alumina matrix composite ceramics used for drawing dies

The alumina matrix ceramics used for drawing dies were prepared by hot-press sintering method. The ceramics materials were made of Al₂O₃/TiC, Al₂O₃/(W,Ti)C and Al₂O₃/Ti(C,N). Mechanical and friction properties of these materials were tested and measured. The experiments for testing friction properties were carried on wear and tear machine. Mechanisms of frictions were analyzed with scanning electron microscope. Results showed that the alumina matrix composite ceramics have good physical and mechanical properties for used as drawing dies. Measured friction coefficients of alumina matrix composite ceramics showed a trend of decline and kept the value of 0.4–0.5 with the rotating speed of 550 rpm. Alumina matrix composite ceramics have smaller wear rate, while the wear rates of Al₂O₃/TiC and Al₂O₃/(W,Ti)C decrease gradually with a rising rotation speed. The wear of alumina matrix ceramics was severe at deformation zone. The primary wear behaviors of alumina matrix ceramics are scraping and furrowing. Even though the mechanisms for wear different, abrasive and adhesive wear were found to be the predominant wear mechanisms for the ceramic drawing die.     

Exploring the influences of the counterpart materials on friction and wear behaviors of atmospheric plasma-sprayed YSZ coating

Sliding wear behaviors of atmospheric plasma-sprayed Yttria Stabilized Zirconia (YSZ) coating mated with four metallic or ceramic counterparts (Si₃N₄, Al₂O₃, GCr15 and ZrO₂) were investigated. It has been found that YSZ coatings in contact with Si₃N₄ and GCr15 show better tribological performances than the other cases, which is due to the formation of the tribolayer mainly consisting of Si₃N₄ and Fe₂O₃ respectively on the worn surfaces. In the case of YSZ coating-Al₂O₃ and YSZ coating-ZrO₂ tribopairs, the wear debris are more irregular and larger in size, resulting in severe abrasive wear and brittle fracture of debris particles. In particular, the specific wear rate of YSZ coating sliding against GCr15 is negative due to the significant material transfer of the tribo-oxide layer, while that of YSZ coating sliding against ZrO₂ is the highest. Amorphization of the wear particles appears in the four cases due to the repeated mechanical action. It has been demonstrated that the wear of YSZ coating deteriorates with the increased flash temperature between the contact surfaces during rubbing process.     

Parametric optimization of dry sliding wear and friction of germanium doped lead calcium titanate borosilicate glass ceramic

In this study, specific wear rate (SWR) and coefficient of friction (COF) of the synthesized samples in 55[(Pb_xCa_1?x)O.TiO₂]?44[2SiO₂.B₂O₃]?1Ge with (0 ≤ x ≤ 0.7 mol%) system of glass ceramics was optimized using Taguchi method. The ASTM standards were used for preparing the samples for friction and wear tests on a pin-on-disc tribometer. The glass ceramic samples were used as pin materials that slid against a disc made up of EN32 steel. For assessing the tribological properties of the glass ceramics, three control factors, viz. material-compositions with varying fraction of x (x = 0.0, 0.1, 0.3, 0.5 and 0.7 mol%), sliding speeds (2.61, 3.14, 3.66, 4.18 and 4.71 m/s) and loads (10, 15, 20, 25 and 30 N) were considered in an L₂₅ orthogonal array design. The optimum input parameters for the minimum SWR and COF were selected based on signal to noise ratios and main effect plots. Analysis of variance (ANOVA) revealed that the sliding speed and lead oxide content of the material are the most contributing factors on SWR and COF, respectively. The optimization for minimizing the SWR and COF was carried out and confirmed. The surface morphologies of the tested glass ceramic sample were studied using scanning electron microscope (SEM) and the elemental analysis of the samples was done using energy dispersive analysis of X-rays (EDAX). The Vickers hardness at the free surface of the glass ceramic samples increased up to 9.59 mol% of lead oxide with the maximum hardness of 23.59 GPa. The compressive strength of glass ceramic samples could reach up to 190 MPa.     

Tribological properties of TiB2 and TiB2–MoSi2 ceramic composites

Recently, dense monolithic TiB₂ and TiB₂–20 wt.% MoSi₂ composites with high hardness (24–26 GPa) have been processed by hot pressing. To assess the tribological potential, the present study was performed in analyzing the influence of load on the fretting wear of TiB₂ and TiB₂–MoSi₂ composites against bearing steel. Under the investigated conditions, a higher coefficient of friction (COF) of 0.5–0.6 was recorded with all the materials with a lower COF at a higher load of 10 N. Detailed microstructural investigation of the worn surfaces was carried out using SEM–EDS and XRD in order to understand the fretting wear mechanisms. Severe wear (order of 10⁻⁵ mm³/N m) was measured for the investigated materials under the selected fretting conditions with lower wear rate for TiB₂–20 wt.% MoSi₂ composite at all loads (2–10 N). While abrasive wear dominates the material removal process in the case of monolithic TiB₂, the tribochemical wear is observed to be the predominant wear mechanism for the composite.     

Microhardness and wear resistance of Al2O3-TiB2-TiC ceramic coatings on carbon steel fabricated by laser cladding

Al₂O₃-TiB₂-TiC ceramic coatings with high microhardness and wear resistance were fabricated on the surfaces of carbon steel substrates by laser cladding using different coating formulations. The microstructures of these ceramic coatings with the different coating formulations were investigated using X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometer. The wear resistance and wear mechanism were analyzed using Vickers microhardness and sliding wear tests. The results showed that when the amount of independent Al₂O₃ was increased to 30%, the ceramic coatings had a favorable surface formation quality and strong metallurgical bond with the steel matrix. The cladding layer was uniformly and densely organized. The black massive Al₂O₃, white granular TiB₂, and TiC distributed on the Fe substrate significantly increased the microhardness and wear resistance. The laser cladding ceramic coating had many hard strengthening phases, and thus resisted the extrusion of rigid particles in frictional contact parts. Therefore, the wear process ended with a “cutting-off” loss mechanism.     

Friction and wear behaviors of dental ceramics against natural tooth enamel

The friction and wear behaviors of dental ceramics against the natural tooth enamel were investigated. In this study three dental ceramics, namely zirconia with both polished and rough surfaces, hot-forged lithium disilicate glass ceramics and silicates based veneer porcelain were involved with two metallic materials, gold–palladium alloy and Nickel–chromium alloy, as references. The tribological tests were carried out under artificial saliva lubrication condition by using freshly extracted natural teeth and samples with controlled surface roughness. The frictional coefficients versus reciprocating cycles were recorded. Scanning Electron Microscopy was used to observe the topography of worn teeth enamel surfaces and antagonists. The frictional coefficient of enamel against gold palladium alloy or Nickel–chromium alloy was the smallest. The frictional coefficient of enamel against polished zirconia or porcelain was between that of metal and glass-ceramic. Upon surface polishing, frictional coefficient between zirconia and enamel was radically decreased. Furrows and granular debris were observed on the worn surfaces of enamel while sliding against the rough zirconia or glass ceramic, indicating a abrasive wear mechanism. While chipping flake and pit-like structure after stripping and crack were observed on the enamel surface while sliding against polished zirconia or Nickel–chromium alloy, indicating a type of fatigue wear. It appeared that the friction and wear performances of zirconia could be improved significantly by adequate surface polishing. This observation indicated that attention must be paid to carefully design proper occlusal surface contours and correctly choose dental materials in clinical practice.     

Wear behavior of plasma sprayed hydroxyapatite bioceramic coating in simulated body fluid

To investigate the wear behavior of bioceramic coating, two-body abrasive wear of air-plasma sprayed (APS) hydroxyapatite (HA) coating was studied in different conditions including: i) in simulated body fluid (SBF) and in dry conditions, and ii) sliding on Al₂O₃ abrasive paper, HA, polycarbonate (PC) and polyurethane (PU), as well as iii) on different applied loads. Cross-sectional microstructures and worn surface morphologies of the coating were examined by scanning electron microscopy (SEM). Phase constitutions were analyzed by X-Ray diffraction (XRD). Microhardness, elastic modulus, fracture toughness and bond strength of the coating were investigated. It was revealed that, under the load of 20?N and sling on different counterpart materials, the wear rates of the coating varied from 24.09?×?10^?2to 0.25?×?10^?2 mg/Nm in SBF and varied from 13.54?×?10^?2 to 0.05?×?10^?2 mg/Nm in dry condition, respectively. The accumulated weight loss of the coating sliding on HA in SBF increased from 3.1 to 7.9?mg as the applied load increased from 5?N to 20?N. As sliding on Al₂O₃ in dry condition and/or under high load, the abrasive wear of the coating dominantly occurred in the form of ploughing and peeling off of splats. As sliding on PC, PU and HA in SBF, the adhesive wear of the coating mainly occurred in the form of exfoliation.     

Fabrication and abrasive wear behavior of ZrO2-SiC-Al2O3 ceramic

In this paper, ZrO₂-SiC-Al₂O₃ ceramic was fabricated by as-prepared ZrO₂-SiC powders and commercial α-Al₂O₃ powders, sintered at 1450 °C for 1 h. ZrO₂-SiC composite powders were synthesized through carbothermal reduction with zircon as raw material and carbon black as the reductant. Through ZrO₂-SiC-Al₂O₃ ceramic mechanical properties measurements it was indicated that this ceramic had excellent properties in both bending strength and hardness. In addition, ZrO₂-SiC-Al₂O₃ ceramic abrasive wear property was measured. ZrO₂-SiC-Al₂O₃ ceramic mass loss increased along with the increase in both wheel rate and applied load. The type of wear particles had an important effect on abrasive wear resistance. ZrO₂-SiC-Al₂O₃ ceramic displayed excellent abrasive wear resistance in bentonite and quartz slurries in comparison with SiC slurry.     

Wear Behavior of Bulk Polycrystalline MgO–MgFe2O4 “Age‐Hardened Alloys”

We report here improved abrasive wear resistances for our newly developed bulk polycrystalline “age‐hardened/toughened” MgO–MgFe₂O₄ “ceramic alloys”. In comparison with phase pure MgO, reductions in wear rates by up to ~30% were recorded for the MgO–MgFe₂O₄ alloys, with those developed upon aging at 1000°C for 0 h showing the best improvements. In contrast to the worn surfaces for MgO, the worn surfaces of the alloys showed the presence of only abrasive grooves with hardly any evidence for brittle fracture induced pull‐out. Estimates for area fractions of pull‐outs and depths of damaged zones present trends similar to the wear rates, with the pull‐out fractions and the depths of damaged zones being lesser for the MgO–MgFe₂O₄ alloys by up to ~60% and ~70%, respectively, as compared to phase pure MgO.     

Friction and wear properties of MoAlB against Al2O3 and 100Cr6 steel counterparts

The present work investigates, for the first time, the dry sliding friction and wear behaviour of fully dense, predominantly single-phase MoAlB ceramics against alumina (Al₂O₃) and 100Cr6 steel counterparts. Against Al₂O₃, the friction coefficient (μ) increased with increasing load and the wear was highly dependent on the load applied. A transition from mild wear under 1 N and 4 N to severe wear at 10 N occurred. Scanning electron microscopy revealed that abrasion is the dominant wear mechanism. Against steel, μ decreased with increasing load and the wear rates were low, under all applied loads. The morphologies of the worn surfaces against steel were characterized by the appearance of a rippled layers. Atomic force microscopy and Raman spectroscopy were used to propose a possible formation mechanism of such patterns. X-ray photoelectron spectroscopy revealed the rippled surfaces to be composed of Fe₂O₃ and a mixture of MoO_x.     

Effects of HfC addition on microstructures and mechanical properties of TiC0.7N0.3-based and TiC0.5N0.5-based ceramic tool materials

Effects of HfC addition on microstructures and mechanical properties of TiC_0.7N_0.3-based and TiC_0.5N_0.5-based ceramic tool materials were investigated. The results showed that the same by-products such as HfN_0.4, HfNi, Ti_0.76Hf_0.24Ni, TiNi_0.85Co_0.15 and HfCo₆ were discovered in these ceramics. To some extent, HfC additive can inhibit their denitrification in the sintering process. The HfC particles can produce the crack flection and a suitable HfC content can improve mechanical properties of these ceramics effectively. Besides, the TiC_0.5N_0.5-HfC ceramics exhibited a poor sinterability compared to TiC_0.7N_0.3-HfC ceramics, showing much more pores in fracture and polished surfaces micrographs; grains in TiC_0.7N_0.3-HfC ceramics are finer than that in TiC_0.5N_0.5-HfC ceramics; the HfC particles dispersion in TiC_0.7N_0.3-HfC ceramics is more uniform than that in TiC_0.5N_0.5-HfC ceramics; thus, the mechanical properties of TiC_0.7N_0.3-HfC ceramics are superior to that of TiC_0.5N_0.5-HfC ceramics. In addition, their fracture mechanism is a combination of transgranular fracture and intergranular fracture. As a consequence, the enhancement of their mechanical properties is conducive to the presence of intermetallic compounds, the fine microstructure and the suitable HfC content.     

Preparation of aluminum reinforced with TiB2-Al2O3-FexAly composites derived from natural ilmenite

Aluminum reinforced with mixed TiB₂-Al₂O₃-Fe _x Al _y ceramic composites was successfully fabricated by squeeze casting of melted Al into a mixed ceramic preform. Mixed TiB₂-Al₂O₃-Fe _x Al _y ceramics have been fabricated in-situ by SHS in the FeTiO₃-B₂O₃-Al system. The reaction was carried out in an SHS reactor under a static argon pressure of 0.5 MPa. The standard Gibbs energy minimization method was used to calculate the equilibrium composition of reacting species. The composites have been subsequently characterized by SEM, image analysis, and XRD. The hardness and wear characteristics of the composites have been investigated. As compared to pure Al, the composite exhibited excellent wear resistance.