Metal matrix composite layers formed by laser processing of commercial purity Ti–SiCp in nitrogen environment

Abstract

Metal matrix composite layer formation by means of laser alloying using 6 μm particle size SiC powder (SiC_p) preplaced on titanium surfaces in a nitrogen environment produced golden coloured tracks and a complete solution of SiC_p in the melt zones under a range of processing conditions. The melt layers consisted of dendrites at the top (titanium nitride based) followed by threadlike particle structures (titanium silicides), and the sizes of dendrites and the threadlike particles werefound to increase with increasing laser power density. The surface layer of the dendrites developed a hardness 4·5–9 times that of the base metal (150 HV), and the deep underlying threadlike structures had a plateau of hardness of aboout 2·8–4 times the base hardness. The metal matrix composite layers were found to be 2–4 times thicker than those produced previously in a helium environment under similar processing conditions. The exothermic reactions due to the formation of titanium nitride, titanium carbide, or titanium carbonitride along with titanium silicide during laser melting of SiC_p coated titanium surfaces under a nitrogen environment are considered to be responsible for the greater melt depth and complete dissolution of ceramic particles, by increasing the temperature of the melt.

MST/3208     

Aerosol synthesis of titanium nitride nanoparticles by direct current arc discharge method

Arc discharge synthesis has industrial relevance due to its low cost and scale-up potential. The production of titanium nitride nanoparticles was achieved by direct current arc discharge in an atmospheric-pressured ambient composed of N₂ and Ar. We systematically investigated the effect of the synthesis parameters, including quench gas velocity, quench gas composition, and applied arc current, on the particle quality, yield, and size. It is found that increasing quench gas velocity enables to produce particles with a primary size of 10–15 nm, while titanium nitride particles of 20–50 nm are produced at low quench gas velocity based on scanning electron microscope (SEM) analysis. X-ray diffraction (XRD) results indicated that titanium nitride particles produced at various nitrogen compositions are almost stoichiometric, while the crystallite size increases almost 20 nm when increasing nitrogen contents in the quench gas. Quench gas composition also has a significant impact on the arc voltage as well as particle production rate. When increasing the nitrogen concentration from 20% to 100%, the production rate can be enhanced by a factor of three. Besides, raising the applied arc current from 12 A to 50 A leads to a yield enhancement of factor 10. According to the Brunauer-Emmett-Teller (BET) measurement, the increase of applied arc current has a limited impact on primary particle size. The enhancement in particle production rate is mainly reflected by the larger agglomerate sizes and agglomerate number concentration. Additionally, based on experimental observations and previous studies, a mechanism is presented to explain the growth of deposits on the cathode tip.     

Self-propagating high-temperature synthesis of ultrafine and nanometer-sized TiC particles

The feasibility of preparing ultrafine and nanometer-sized titanium carbide particles by self-propagating high-temperature synthesis (SHS) has been studied. Data are presented on the structure formation of TiC powders during SHS with a reduction step. Basic to this process is an exothermic reaction between titanium dioxide, magnesium metal, and carbon. The effects of the composition of the starting mixture, relationship between its components, and the morphology and particle size of the starting TiO₂ powder on the particle size of the forming material have been investigated. The TiC powder was recovered from the sinter cake by chemical dispersion, a chemothermal treatment of the synthesis product in different solutions. The results demonstrate that treatment of the sinter cake with appropriate solutions removes impurities and causes imperfect intergranular layers to dissolve. As a result, the cake breaks down into homogeneous single-crystal particles. Subsequent treatment in different solutions further reduces the particle size of the powder. The effect of the composition of the dispersing solution on the particle size of the TiC powder has been studied. Our results made it possible to identify conditions for the preparation of titanium carbide powders containing up to 70% of particles less than 0.3 μm in size by SHS followed by chemical dispersion.     

The synthesis of ultrafine titanium nitride in an r.f. plasma

The ultrafine titanium nitride particles with a statistical median size of about 10 nm were prepared by passing pure titanium powder (<25 m) through a radio-frequency (r.f.) argon-nitrogen plasma. The effects of the [N₂]/[Ti] molar ratio of the reactant on the nature of the products were investigated by chemical analysis, X-ray diffraction and electron microscopy. The conversion efficiency was close to 100%. The colour of the product was black, which is attributed to the particle size ranging from 5 to 150 nm. Most of the crystallites were single crystal and showed clear-cut habits of cubic phase. The chemical composition and lattice parameter of the products changed with the [N₂]/[Ti] ratio. The thermodynamics of the process were also considered. These results provide evidence to suggest that new materials can be produced by an r.f. plasma process, in particular, the ultrafine refractory nitrides.     

Al–Ti powder produced through mechanical alloying for different times

A powder mixture of aluminum, 10 wt% titanium, and 1.5 wt% of a wax acting as process control agent (PCA), has been attrition-milled for 2–20 h. Titanium powder had been previously ground to a lower particle size to make it similar to the as-received aluminum particle size. The overall aim of this work was to achieve a metastable titanium solution in the aluminum matrix. Changes with milling time of particle size and shape, microstructure, hardness and other powder characteristics have been studied. Given the used experimental-conditions, a process time of 10 h has been selected for the mechanical alloying (MA) of Al–10Ti powder, attaining a compromise between uniform microstructure development and a not so long processing time. At this milling time aluminum dissolves about 9 wt% Ti, increasing its Vickers microhardness (202 VH₂₀) more than 10 times with reference to the starting Al powder (20 VH₂₀). Milled particle size is smaller than the starting one (17 vs. 44 μm). Increasing milling for longer times, up to 20 h, does not produce important changes in powders structure.     

Preparation of titanium nitride coated powders by rotary powder bed chemical vapour deposition

Titanium nitride coated powders were prepared by rotary powder bed chemical vapour deposition (CVD) in which a powder in a rotary specimen cell was heated by infrared radiation in a reactant gas stream. Titanium powder covered with TiN or Ti₂N thin film was obtained by diffusion coating treatment of titanium particles (grain size 10 to 50 µm) at 900 to 1000°C and 0.5 to 1.0 atm for 60 min in a nitrogen stream. TiN was coated on to the surface of scaly graphite particles (grain size 30 to 100 µm or 100 to 1000 µm) as well as titanium particles by CVD in the reactant system TiCl₄-N₂-H₂ at 900° C and 1 atm for 40 min. The uniformity of the coating (composition and film thickness) and the dispersability of the coated particles were considerably promoted by rotating the powder bed at about 90 r.p.m. compared with nonrotary powder bed CVD.     

Mechanochemical synthesis and shock wave consolidation of TiN(Al) nanostructure solid solution

This paper aims to report the study of the synthesis of a titanium nitride nanostructure solid solution through the reduction of aluminum nitride with titanium based on the stoichiometric reaction of 2Ti + AlN by mechanical alloying (MA) process at a ball-to-powder weight ratio of 15:1. A nanostructure solid solution of in-situ titanium nitride was formed through exchange reaction between Ti and AlN at the initial time of MA. XRD, SEM, EPMA, TEM, and particle size analysis (PSA) were used to characterize the products. It was found that the amount of Al resulting from decomposition of aluminum nitride dissolved in the TiN lattice increased in accordance with milling time, leading to the formation of TiN(Al) solid solution and a reduction of the TiN lattice interplanar distance. The milled powder displayed equiaxed morphology and a narrow size distribution of about 1 μm at the end of the milling process. In-situ TiN(Al) crystallites were of an average size of 6 ± 2 nm. Subsequent to MA, an underwater shock compaction method was applied to the prolonged milled powders to obtain bulk sample. The effect of this shock compaction on the selected sample resulted in the preservation of its nanostructure characteristics with no additional phase transformation which are considered advantageous in the use of high dynamic compaction method for ceramic materials.     

等离子体法制备超细粉体氮化铝的研究

以微米级铝粉为原料 ,用N2 热等离子体法制备了超细氮化铝粉体。在等离子体功率12kW ,运行N2 流量 2m3/h ,急冷NH3流量 0 6m3/h ,送粉N2 流量 0 8m3/h条件下 ,铝粉全部转化为纳米氮化铝。采用SEM技术和粒度分析仪对产品进行了分析 ,制得的氮化铝粉末平均粒径为10 0nm ,粒度分布为 4 0～ 14 0nm     

Assessment of the effect of particle size on the rate of temperature alignment in systems used for shock-wave synthesis of diamond,cubic boron nitride,and γ-silicon nitride,based on a simple model

The change in the spatial distribution of relative temperatures in the system of a spherical particle located in the center of a spherical matrix is simulated. Silicon nitride (Si₃N₄) and boron nitride (BN) are considered in a matrix of potassium bromide (KBr); graphite, diamond, and silicon nitride are studied in a copper matrix. Calculations are performed for the four sizes of particles: 1, 5, 20, and 100 μm. It is shown that the temperature is equalized by approximately 80% in 1 μs in the particles of Si₃N₄ and BN with a size of 5 μm in the KBr matrix. In the system of silicon nitride–copper, such alignment is performed for a particle with a diameter of 20 μm. For a diamond particle in the copper matrix, the particle size may be even greater. The particle sizes for which calculations showed a rather high rate of heat transfer in a time of ~1 μs either match or are somewhat larger than the particles of diamond, cubic boron nitride, and γ-silicon nitride formed during the real shock-wave synthesis of these materials.     

Comparison of deoxidation capability on the specific surface area of irregular titanium powder using calcium reductant

Irregular titanium powders of various particle size in the range 60–250?μm were deoxidized using calcium as the reductant, and the effect of specific surface area on the process was investigated. At 1273?K, the oxygen concentration was reduced from 0.2840?wt% to 0.0950?wt%, from 0.2050?wt% to 0.0825?wt%, and from 0.1700?wt% to 0.0825?wt% in titanium powders with average particle sizes of 60?μm, 125?μm, and 250?μm, respectively, and the corresponding removal degree of oxygen (RDO) for these specimens was determined to be 66.5%, 59.7%, and 51.4%; that is, the RDO was inversely proportional to the average particle size of the irregular titanium powder. It was confirmed that the specific surface area of the titanium powder available for reaction with calcium, was the critical factor in the deoxidation of titanium powder using calcium as reductant.     

钛粉对电子雷管电引火药头性能的影响

在普通电雷管电引火药头的基础配方中添加钛粉,研制电子雷管用电引火药头,研究钛粉含量和粒度对电引火药头发火时间的影响。试验结果表明:在一定范围内,随着钛粉含量的增加,药头体系能量增大,传热效率提高,药头发火时间变短,精度和一致性提高。钛粉粒径减小,比表面积增大,电引火药头中点火药颗粒间反应速率增大,发火时间缩短,发火一致性提高。DSC数据表明,外加15%(质量分数)钛粉的配方比基础配方点火药起始分解温度提前5.4 ℃,放热分解峰温提前15.9 ℃。     

Self-propagating high-temperature synthesis of titanium nitride with the participation of ammonium chloride

We have studied the combustion of titanium in nitrogen in the presence of ammonium chloride. It has been shown that the use of NH₄Cl in the self-propagating high-temperature synthesis of TiN considerably reduces the combustion temperature, prevents sintering of the synthesized titanium nitride particles, and increases their specific surface area. The synthesis products have the form of nanostructured titanium nitride particles which reproduce the shape of the starting titanium particles but consist of equiaxed titanium nitride grains ranging in size from 50 to 500 nm. We have obtained nanostructured titanium nitride powders ranging in specific surface area up to 80 m²/g.     

Development of Wear and Corrosion Resistant Metal Matrix Composites with hard Particles formed in Situ

Metal matrix composites (MMC) were developed, consisting of hardenable steel matrices and embedded particles of titanium nitride (TiN) or vanadium nitride (VN) formed in situ during the consolidation by hot isostatic pressing (HIP). Designing wear and corrosion resistant materials was the objective of this development. The materials were produced by means of powder metallurgy and are composed of a ferrritic stainless steel powder X4CrMo15–1 and crushed particles of ferro titanium or ferro vanadium, respectively. These powder mixtures were first heat treated in an N₂‐atmosphere for alloying with nitrogen and subsequently consolidated to wear resistant MMC by HIP. This publication describes the necessary processing steps, taking into account thermodynamic equilibrium calculations with Thermo‐Calc.     

Tailoring size of BaTiO3 nanocrystals via ambient conditions sol process

As the miniaturization of electronic devices continues to demand smaller and uniform particle size of the powders, size control of the powder becomes critical. Under carefully controlled experimental conditions, nanocrystalline BaTiO₃ particles have been prepared by ambient condition sol process. Soluble precursors of barium and titanium in water have been used to produce a mixed metallic gel using KOH as the mineralizer. The gel was peptized and crystallized in water under refluxing condition. The effect of various experimental parameters such as the starting Ba/Ti ratio, temperature, time, and additives on the size of the crystallites have been investigated. A higher Ba/Ti ratio in the precursor solution led to smaller crystallite sizes of BaTiO₃ particles. A higher temperature of refluxing had a positive effect of producing smaller crystallites, as well as particle sizes of the resulting powder. Using a polymeric surface modifier during BaTiO₃ synthesis led to a smaller particle size and increased re-dispersibility of the particles in water. The duration of refluxing was determined to have a minimal effect on the resulting particle size. The powders have been characterized by X-ray diffractometry for phase purity, and by dynamic light scattering for particle size. Field emission scanning electron microscopy and transmission electron microscopy have been utilized to examine the morphology of the particles.     

Fabrication of a composite powder and its application as an active brazing alloy

A copper-based active brazing alloy containing a high titanium content was produced by an electroless coating technique. Particles with a narrow density distribution were produced by deposition of nano-copper on a fine titanium powder. Both conventional titanium powder and sponge titanium were studied. The effects of pH and time on copper deposition were investiguated.Higher pH was found to increase the quantity of copper deposited. Using multiple depositions, a copper-titanium ratio of 75 wt% copper-25 wt% titanium could be achieved after several platings for pH varying between 12 and 12.8. The particle size distribution of the composite powder shows uniform growth of the copper shell and no agglomeration under pH 12. Major agglomeration of the final powder was observed for a bath pH of 12.8.Complete melting of the composite powder has been studied by DSC and the sessile drop technique. Melting began within the diffusion zone formed at the interface through the Cu₄Ti → Cu(s) + L peritectic reaction that occurs at 885^∘C. The melting process continued by successive peritectic reactions and dissolution of the remaining elements of the diffusion couple. The wetting behavior of this alloy was evaluated on different ceramic substrates (Al₂O₃, Si₃N₄) and found to be similar to literature observations.     

Preparation of powder barium titanate

Phase-pure BaTiO₃ powder (free of Ba₂TiO₄, BaCO₃, Ba(NO₃)₂, and OH impurities) with an average particle size of about 100 nm is prepared by solid-state reaction between titanium oxyhydroxide and barium hydroxide ground and mixed by sonication in an inert organic liquid.     

Synthesis of TiB2 powder from a mixture of TiN and amorphous boron

TiB₂ powder was synthesized by solid state reaction using amorphous boron and TiN as a source of titanium. The TiB₂ formation did not occur at all in a nitrogen atmosphere even at 1400° C. TiB₂ formed above 1100° C in argon and hydrogen atmospheres. The only crystalline phase of TiB₂ powder was favourably synthesized at 1400° C for 360 min in an argon atmosphere from a starting powder with a composition containing excess boron (B/Ti = 2.2). The synthesized powder was well dispersed and had a particle size of 0.5 to 2 µm. The powder activity was evaluated by sintering at 4 G Pa and 1300 to 1600° C for 15 min.     

Preparation of Ultrafine Boron Nitride Powders by Self-propagating High-Temperature Synthesis

The possibility of preparing ultrafine boron nitride powders by self-propagating high-temperature synthesis (SHS) is examined. The results demonstrate that, by varying SHS conditions (starting-mixture composition, combustion rate, cooling rate, and intermediate grinding time), one can control the morphology and particle size of the resultant hexagonal BN powder. Systematic data are presented on the chemical dispersion of SHS products for separating nanometer-sized particles. The effect of chemical dispersion (composition of the dispersion medium, process temperature, and dispersion time) on the particle size, morphology, and chemical and phase compositions of boron nitride powders is analyzed. Hexagonal boron nitride powders are obtained with a purity of 99.5+%, particle size of 0.1–0.2 m, and specific surface of up to 65 m²/g.     

固相反应法合成碳化硼纳米粉体

以六方氮化硼和炭黑(或石墨)为原料, 采用固相反应法合成了碳化硼粉体. 碳源、反应气氛和温度对粉体合成产生重要影响. 以炭黑为碳源, 在1900℃真空下保温5 h, 得到了平均粒径约为100 nm的碳化硼纳米粉体. 与商业粉体相比, 合成的粉体具有较好的烧结活性. 在2000℃/30 MPa/1 h条件下烧结, 样品的相对密度达到97.9%(商业粉体样品为93.1%), 这可归结于合成的粉体具有细小的粒径、低的氧含量和一定程度的孪晶结构.     

Preparation and characterization of YBa2Cu3O7−x powder by the ultrasonic spray pyrolysis method

A single-phase YBa₂Cu₃O_7−x powder was prepared in an air flow system by thermally decomposing droplets containing the nitrate salts of yttrium, barium and copper in distilled water. The powder obtained had a mean particle size 0.78 μm and a very narrow particle size distribution. The total porosity of the powder was estimated to be about 63%. It was found that much agglomeration had occurred among the droplets, which would have an adverse effect on the particle size distribution. The bulk density of a sintered specimen using the powder prepared at 950 °C was higher than 97% theoretical density.