TiC Composites Research Articles

Population Dynamics and Within-Tussock-Succession in a Carex sempervirens Subalpine Grassland in the Swiss Alps

Tussock-forming graminoids play an important role in high-altitude grasslands. In tussocks many other plant species can grow, forming small communities. However, little is known about such small-scale vegetation, especially dur- ing succession. In an abandoned subalpine pasture in the Swiss National Park, we studied population dynamics and within-tussock vegetation of Carex sempervirens in four successional grassland stages (i.e. early, young, mature and se- nescent) distinguished at community level. At population level, we observed a succession process encompassing both di- rectional and cyclic elements. In agreement with a decrease in grazing pressure and tussock vitality, similarity of the vege- tation within tussocks decreased from the early to the senescent stage. Within-tussock vegetation of the early stage was more similar to that of the young stage than to that of the mature and the senescent stage. Fuzzy ordination revealed a similar pathway of succession in C. sempervirens tussocks as observed at community level. We conclude that succes- sional transition from grassland to forest may encompass more than one C. sempervirens cycle and with each cycle floris- tic composition both inside and outside C. sempervirens tussocks will become more similar to the subsequent forest stage.

Preparation and mechanical properties of Fe 3Al(Ti)/TiC composites

Near fully dense Fe 3Al(10Ti)/TiC composites were synthesized by MA and hot-pressing sintering methods. Based on the Orowan strengthening effect offered by the nano-TiC particles, higher three-point bending strength and hardness values, 1310 MPa and 90 HRA, were achieved in Fe 3Al(10Ti)/40 vol%TiC composite. The addition of Ti favored the improvement of hardness and room temperature bending strength of composites by the ordering strengthening effect and solid solution hardening effect. The microstructures of as-synthesized composites were investigated by XRD, SEM and TEM. Fe 3Al particles had equiaxed morphology. TiC particles with grain size ranging from 50 to 200 nm were homogeneously dispersed in Fe 3Al matrix. The larger TiC particles with sub-micrometer were mainly located at grain boundaries and the smaller ones were within matrix grains.

Characterization of laser powder deposited Ti–TiC composites and functional gradient materials

Laser powder deposition (LPD) is an important process for the preparation of functional gradient materials due to its unique layer-by-layer additive manufacturing character. In this paper, based on preliminary experiments and analysis of LPD Ti–TiC composites with different premixed ratios of Ti to TiC, two thin walls of functional gradient material of Ti to Ti–40vol.%TiC were successfully deposited by adjustment of processing parameters and real-time variation of the feeding ratio of Ti to TiC during LPD process. The tensile strength of LPD deposited Ti–TiC composites changed marginally with TiC content, while the ductility displays a sharp reduction with increase in TiC addition. The wear resistance under dry sliding wear test can be improved with addition of TiC. Microstructure observation and hardness testing performed along the composition gradient direction indicated that functional gradient materials of Ti to Ti–40vol.%TiC without a discrete interface could be easily obtained through this process.

Effect of TiC content on the microstructure and properties of Ti 3SiC 2–TiC composites in situ fabricated by spark plasma sintering

Spark plasma sintering technique was used to in situ fabricate high dense Ti 3SiC 2–TiC composites. The calculated TiC volume content from X-ray diffraction (XRD) is close to the theoretical one. It is found from fracture surface observation that TiC is about 1 μm, and Ti 3SiC 2 is about 2–10 μm in grain size. The fracture modes consist of intergranular mainly for Ti 3SiC 2 and transgranular fracture mainly for TiC. With the increasing of TiC volume content, Vickers hardness increases to the maximum value of 13 GPa for Ti 3SiC 2-40 vol.%TiC. Fracture toughness and flexural strength of the composites are also improved compared with those of monolithic Ti 3SiC 2 except for Ti 3SiC 2-40 vol.%TiC composite. The main reasons for the sudden decrease of fracture toughness and flexural strength of Ti 3SiC 2-40 vol.%TiC composite can be attributed to the relatively lower density, some clusters of TiC in the composite and the transition of fracture mode from intergranular to transgranular. The thermal conductivities decreased with the addition of TiC. The minimum thermal conductivity is 22 W m °C −1 for Ti 3SiC 2-40 vol.%TiC composite.

Chemical bonding states of TiC films before and after hydrogen ion irradiation

TiC films deposited by rf magnetron sputtering followed by Ar+ ion bombardment were irradiated with a hydrogen ion beam. X-ray photoelectron spectroscopy (XPS) was used for characterization of the chemical bonding states of C and Ti elements of the TiC films before and after hydrogen ion irradiation, in order to understand the effect of hydrogen ion irradiation on the films and to study the mechanism of hydrogen resistance of TiC films. Conclusions can be drawn that ion bombardment at moderate energy can cause preferential physical sputtering of carbon atoms from the surface of low atomic number (Z) material. This means that ion beam bombardment leads to the formation of a non-stoichiometric composition of TiC on the surface. TiC films prepared by ion beam mixing have the more excellent characteristic of hydrogen resistance. One important cause, in addition to TiC itself, is that there are many vacant sites in TiC created by ion beam mixing. These defects can easily trap hydrogen and effectively enhance the effect of hydrogen resistance.

Damage evaluation in discontinuously reinforced aluminum matrix composites subjected to thermal cycling

A comparative study of the damage in the powder metallurgy processed Al–Cu–Mg alloy–SiC (as-extruded and solution-treated) and Al–SiC (hot rolled), and in situ cast Al–TiC (as-extruded) composites, each with 15 vol.% particulate reinforcements, has been carried out. Repeated thermal cycling of the composites between 500 and 0 °C was followed by evaluation of damage by examination of microstructure using scanning electron microscopy, determination of changes in dynamic Young's modulus, and measurement of microhardness near the reinforcement–matrix interfaces. The thermally cycled Al alloy–SiC composites have exhibited reduction in Young's modulus and microhardness adjacent to reinforcement–matrix interfaces, due to decohesion caused by thermal mismatch strains. In contrast, the SiC or TiC reinforced Al composites subjected to thermal cycling, have shown only a marginal reduction in the Young's modulus, and cracks in the Al matrix rather than at interfaces, near which microhardness increment by strain-hardening through dislocation generation has been noticed.

RETRACTED: Influence of cobalt phase on thermal shock resistance of Al2O3–TiC composites evaluated by indentation technique

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy).This article has been retracted at the request of the Editor-in-Chief.The corresponding author of this article informed Materials Research Bulletin on 1 August 2014 of the existence of a very similar paper, written in Chinese by the same group of co-authors and published in the Journal of Inorganic Materials (2007, 22(1), 106-112) by The Science Press. In the view of Materials Research Bulletin, authors have a responsibility not to engage in redundant publication, which occurs when two or more papers share the same hypothesis, data, discussion points, or conclusions - all of which overlapped in these two papers. In particular, figures 2, 3, 4, 5, and 7 as well as table 4 in the Materials Research Bulletin paper all appear in the earlier Chinese work as figures 5, 6, 1, 8, and 4 and table 4. Such redundancy is not only a violation of the copyright held by Journal of Inorganic Materials, but is an affront to scientific publishing ethics. The editorial board and publishers of Materials Research Bulletin are grateful to the authors for bringing this situation to our attention.

방전 플라즈마 소결에 의한 Distaloy AE-TiC 써멧의 치밀화 특성

The fabrication of Fe alloy-40 wt.%TiC composite materials using spark plasma sintering process after ball-milling was studied. Raw powders to fabricate Fe alloy-TiC composite were Fe alloy, and activated carbon. Fe alloy powder was Distaloy AE (4%Ni-1%Cu-0.5%Mo-0.01%C-bal.%Fe) made by Hoeganes company with better toughness and lower melting point. These powders were ball-milled in horizontal attrition ball mill at a ball-to-powder weight ratio of 30 : 1. After that, these mixture powders were sintered by using spark plasma sintering apparatus for 5 min at in vacuum atmosphere under torr. DistaloyAE-40 wt.%TiC composite was directly synthesized by dehydrogenation and carburization reaction during sintering process. The phase transformation of as-milled powders and sintered materials was confirmed using X-ray diffraction (XRD) and transmission electron microscope (TEM). The density and harness materials was measured in order to confirm the densification behavior. In case of DistaloyAE-40 wt.%TiC composite retained for 5 min at , it has the relative density of about 96% through the influence of rapid densification and fine TiC particle reinforced Fe-based composites materials.

Microstructure and formation mechanism of titanium matrix composites coating on Ti-6Al-4V by laser cladding

Laser cladding experiments were done on a 5-kW continuous wave CO 2 laser to synthesize TiC and TiB reinforced titanium matrix composite coatings on Ti-6Al-4V alloy with a mixture of Ti and B 4C precursor powder. The thermodynamics of the reactions were calculated and analyzed. The microstructure and phase evolution of TiB and TiC composites were investigated. The results showed that the chemical reaction between Ti and B 4C would release much heat, and these compounds, TiC, TiB, and small amount of TiB 2, can be formed on the surface of Ti-6Al-4V alloy if the supplied energy is sufficient to excite the reaction among the initial products. A good metallurgical bond between the coating and the substrate can be achieved. The microhardness of coating was irregular and the maximum value was approximately HV600.

Microstructure, Phase and Thermoelastic Properties of Laminated Liquid‐Phase‐Sintered Silicon Carbide–Titanium Carbide Ceramic Composites

Hot‐pressed silicon carbide–titanium carbide (SiC—TiC) composites sintered with liquid‐phase forming Al2O3 and Y2O3 mixtures have been studied. Samples were fabricated by successively stacking tape‐cast sheets of a single composition, resulting in a laminated body of uniform composition. This approach required the development of a technology easily transferable into the production of functionally graded SiC–TiC materials. The effects of this processing route on the resultant microstructures and phases were explored in detail. Additionally, because of the consequences for graded materials, the effects of TiC proportion on the thermal expansion coefficients, Young's modulus, and Poisson's ratios for several SiC–TiC composites were also determined.

Al 2O 3–TiC–ZrO 2 nanocomposites fabricated by combustion synthesis followed by hot pressing

Al 2O 3–TiC–ZrO 2 nanocomposites were prepared by combustion synthesis followed by hot pressing with TiO 2, Al, C and ZrO 2 as raw materials. Combustion synthesis is favorable to obtain in situ formed powder with TiC and ZrO 2 nanoparticles distributed in Al 2O 3 matrix. The effects of varying amount of ZrO 2 nano-scale additives on the mechanical properties and microstructure of Al 2O 3–TiC composite were studied. An appropriate amount of ZrO 2 nanoparticle additive improves the mechanical properties. The flexural strength and fracture toughness of Al 2O 3–TiC–10 wt.% ZrO 2 composite were approximately 20% higher than that of Al 2O 3–TiC composite. The addition of ZrO 2 nanoparticles reduced the grain size and improved the distribution of different phases. With the ZrO 2 addition, the fracture mode changes from intergranular to mixed inter/transgranular fracture. The residual stresses are generated by the thermal expansion coefficient mismatch between different phases, which leads to the generation of dislocations and microcracks around the nanoparticles. The effects of nanoparticles on the deflected propagation, nailing and blocking of the dislocation and microcracks are believed to contribute to the improvement of the strength and toughness of Al 2O 3–TiC–ZrO 2 composite.

Simulation of KrF laser ablation of Al 2O 3–TiC

Previous work by the authors on micromachining of Al 2O 3–TiC ceramics using excimer laser radiation revealed that a columnar surface topography forms under certain experimental conditions. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) observations show that the columns develop from small globules of TiC, which appear at the surface of the material during the first laser pulses. To understand the mechanism of formation of these globules, a 2D finite element ablation model was developed and used to simulate the time evolution of the temperature field and of the surface topography when a sample of Al 2O 3–TiC composite is treated with KrF laser radiation. Application of the model showed that the surface temperature of TiC rises much faster than that of Al 2O 3, but since TiC has a very high boiling temperature, its vaporization is significant only for a short time. By contrast, the surface temperature of Al 2O 3 rises above its boiling temperature for a much longer period, leading to a greater ablation depth than TiC. As a result, a small TiC globule stands above the Al 2O 3 surface. The results of the model are compared with experimental measurements performed by AFM. After three pulses, the height of the globules predicted by the model is about 340 nm, in good agreement with the height measured experimentally, about 400 nm.

TiC reinforced composite layer formation on Al–Si alloy by laser processing

Al–Si alloy was laser surface treated with various compositions of TiC and Ni under different laser processing parameters to produce a TiC reinforced composite layer on it. The study shows that TiC composite layer is formed when the composition is 75TiC–25Ni (wt-%) and laser power 2·5 kW and scan speed 0·2 m min−1. The layer exhibited an average microhardness of ∼750 HV, which is free from pores as well as cracks and contained TiC and Al–Si phases distributed in the Ni–Al matrix. Mechanical strength of layer is studied by the hardness test.

In-situ production of Fe–TiC composite

A TiC/Fe composite was produced by a novel process which combines in situ with powder metallurgy techniques. The microstructure of the Fe–TiC composite was studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD); with the help of differential thermal analysis (DTA), the reaction path of the Fe–Ti–C system was discussed. The results show that the production of an iron matrix composite reinforced by TiC particulates using the novel process is feasible. TiC particles exhibit homogeneous distribution in the α-Fe matrix. The reaction path is as follows: first, allotropic change Fe α → Fe γ at 765.6 °C; second, formation of the compound Fe 2Ti at 1078.4 °C because of the eutectic reaction between Ti and Fe; third, reaction between carbon and melted Fe 2Ti causing formation of TiC at 1138.2 °C; finally, Fe 3C formation due to the eutectic reaction between remanent C and Fe at 1146.4 °C.

The Effect of MgO-Y<sub>2</sub>O<sub>3</sub> on Al<sub>2</sub>O<sub>3</sub>-TiC Composites

The effect of the additives, Y2O3 and MgO, on the sintering and properties of Al2O3-TiC composites was investigated. It is known that MgO is used as additive for improving densification and Y2O3 is applied as sintering aid. In this study, the amounts of TiC were varied in the range of 30-47 wt%. The 0.5 wt% MgO and also varied amounts of Y2O3 from 0.3 to 1 wt% were added into the composites. The sintering of Al2O3-TiC composites was performed in a graphite- heating element furnace at different sintering temperature, 1700 and 1900°C, for 2 hr under an argon atmosphere. The results demonstrated that the properties of the composites sintered at 1700°C were much better than those sintered at 1900°C. The comparisons on physical properties, mechanical properties and microstructure of composites with and without additives were reported. Comparing with other samples, Al2O3-30wt%TiC composites with 0.5wt% MgO and 1 wt%Y2O3 exhibited the highest density of approximately 98% of theoretical and flexural strength of 302 MPa.

Effect of MgO-Y2O3 Powders and Sintering Temperature on Properties of Al2O3-TiC Composites

Al2O3-30%TiC composites doped with 0.5%MgO and 0.3-1.0% Y2O3 additives are pressureless-sintered at different conditions such as temperatures, soaking times, and heating rates under an argon atmosphere. The physical, mechanical properties, and cutting performance of sintered composites were compared with commercial one. In this work, the Al2O3-30%TiC composites doped with 0.5%MgO and 0.3%Y2O3 sintered at 1800°C obtained highest density of 97% of theoretical and flexural strength of 343 MPa. In addition, the cutting performance of the Al2O3-30%TiC-0.5%MgO-0.3%Y2O3 sintered at 1800°C was comparable with the commercial cutting tool.

탄화 티타늄 금속기 복합재에 대한 상대재의 마모거동

Wear of steel plate was measured during unlubricated sliding against TiC composites. These composites consist of round TiC grains and steel matrix. TiC grain itself exhibits low surface roughness and round shape, which does not bring its counterpart into severe damage from friction. In our work a classical experimental design was applied to find out a dominant factor in counterpart wear. The analysis of the data showed that only the applied load has a significant effect on the counterpart wear. Wear rate of counterpart increased non-linearly with applied load. Amount of wear was discrepant from expectation of being in proportion to the load by analogy with friction force. Our experimental result from treating matrix variously revealed bimodal wear behavior between the composites and counterpart where a mode seems to result from the special lubricant characteristic of TiC grains, and the other is caused by metal-to-metal contact. The two wear mechanisms were discussed.

Thermodynamic and lattice parameter calculation of TiC x produced from Al-Ti-C powders by laser igniting self-propagating high-temperature synthesis

TiC x has been formed by self-propagating high-temperature synthesis (SHS) from elemental powder mixtures with a range of C/Ti ratios. The combusting behavior of the powder mixtures was investigated. The effect of the processing variables on the lattice parameter and the composition of TiC were examined. The results show that lattice parameters of TiC x increase with the increase of C/Ti ratio. The variation of Gibbs free energy in Al-Ti-C system was studied based on the thermodynamics theory. The results show that TiC and Al 3Ti phases are easier to form than Al 4C 3 phase.

Multifunctional biocompatible nanostructured coatings for load-bearing implants

To take advantage of the self-propagating high-temperature synthesis (SHS) technique, magnetron sputtering (MS), and ion implantation assisted magnetron sputtering (IIAMS), a new type of biocompatible nanostructured film was developed and studied. Films of Ti–Ca–C–O–(N), Ti–Ca–P–C–O–(N), Ti–Si–Zr–O–(N), and Ti–Zr–C–O–(N) were deposited by DC MS or IIAMS of SHS composite targets TiC 0.5 + CaO, TiC 0.5 + CaO + TiO 2, TiC 0.5 + Ca 10(PO 4) 6(OH) 2, Ti 5Si 3 + ZrO 2, and TiC 0.5 + ZrO 2 in an Ar atmosphere or reactively in a gaseous mixture of Ar + 14% N 2. The films were characterized in terms of their structure, chemical, mechanical, and tribological properties. The biocompatibility of the films was evaluated by both in vitro and in vivo experiments. In vitro studies involved the investigation of adhesion, spreading and proliferation of Rat-1 fibroblasts, MC3T3-E1 osteoblasts, and IAR-2 epithelial cells, morphometric analysis, actin cytoskeleton and focal contacts staining of the cells cultivated on the films. Alkaline phosphatase activity and von Kossa staining of osteoblastic culture were investigated. Three groups of the in vivo investigations were fulfilled. Teflon plates coated with the tested films were inserted subcutaneous in mice and analysis of the population of cells on the surfaces was performed. Implantation studies of Ti rings and Ti rods coated with tested films using rat calvarian and hip defect models were also fulfilled. The results obtained show that Ti-based multicomponent films possess a combination of high hardness and adhesion strength, reduced Young's modulus, low wear and friction, high corrosion resistance with bioactivity, biocompatibility and non-toxicity that makes the films promising candidates as tribological coatings to be used for various medical applications like orthopedic prostheses, materials for connective surgery and dental implants.

Stainless steel binder for the development of novel TiC-reinforced steel cermets

Steel reinforced TiC composites are an attractive choice for wear resistance and corrosion resistance applications. TiC-reinforced 17-4PH maraging stainless matrix composites were processed by conventional powder metallurgy (P/M). TiC-reinforced maraging stainless steel composites with >97% of theoretical density were fabricated. The microstructure, mechanical and wear properties of the composites were evaluated. The microstructure of these composites consisted of spherical and semi-spherical TiC particles. A few microcracks appeared in the composites, showing the presence of tensile stress in the composites produced during sintering. Typical properties, namely, hardness and bend strength were reported for the sintered composites. After heat treatment and aging, the increase of hardness was observed. The increase of hardness was attributed to the aging reaction in the 17-4PH stainless steel. The precipitates appeared in the microstructure and were responsible for the increase in hardness. The specific wear behavior of the composites was strongly dependent on the content of TiC particles, the interparticle spacing, and the presence of hard precipitates in the binder phase.