Effect of B/C ratio on the microstructure and grain refining efficiency of Al-Ti-C-B master alloy

A series of Al-Ti-C-B master alloys with different B/C ratios were prepared in the present study. It was found that with the increase of B/C ratio, the microstructure of Al-Ti-C-B was improved firstly and then became agglomerated at a very high B/C ratio. Furthermore, the grain refining performance of Al-Ti-C-B also varied with the increase of B/C ratio. The experimental results show that Al-Ti-C-B master alloy presents both a dispersive microstructure and a high grain refining efficiency at an optimum B/C ratio about 1/1. It is supposed that the improvement of Al-5Ti-0.25C-0.25B master alloy can be attributed to the high efficiency TiC_xB_y particles and a certain amount of TiB₂ particles.     

Effects of CeO2 additive on the microstructure and mechanical properties of in situ TiB2/Al composite

In this paper, CeO₂ was investigated as an additive for in situ preparation of TiB₂/Al composite using an exothermic reaction process via K₂TiF₆ and KBF₄ salts. Experimental results indicated that when 0.5 wt.% CeO₂ additive was added, the dispersion of TiB₂ particles was improved significantly. Meanwhile, α-Al matrix grain was further refined. Compared with the composite without CeO₂, the ultimate tensile strength, yield strength, elastic modulus and tensile elongation increased by 8%, 7%, 26% and 14%, respectively in as-cast condition, and the tensile fracture behavior of the composite with CeO₂ belonged to a typical ductile fracture with microvoid coalescence.     

Effects of C/B4C ratio on microstructure and property of Fe-based alloy coating reinforced with in situ synthesized TiB2-TiC

The Fe-based alloy coatings reinforced with in situ synthesized TiB₂-TiC were prepared on Q235 steel by reactive plasma cladding using Fe901 alloy, Ti, B₄, and graphite(C) powders as raw materials. The effects of C/B₄C weight percentage ratio(0-1.38) on the microstructure, microhardness, and wet sand abrasion resistance of the coatings were investigated. The results show that the coatings consist of (Fe, Cr) solid solution, TiC, TiB₂, Ti₈C₅, and Fe₃C phases. The decrease of C/B₄C ratio is propitious to the formation of TiB₂ and Ti₈C₅. Increasing the C/B₄C ratio can help to refine the microstructure of the coatings. However, the microhardness of the middle-upper of the coatings and the wet sand abrasion resistance of coatings degenerate with the increase of C/B₄C ratio. The coating exhibits and the wet sand abrasion resistance at C/B₄C=0 and its average mass loss rate per unit wear distance is 0.001 2%/m. The change of the wet sand abrasion resistance of the coatings with C/B₄C ratio can be mainly attributed to the combined action of the changes of microhardness and the volume percentage of the ceramic reinforcements containing titanium in the coatings.     

Microstructural and mechanical evaluation of Al-TiB2 nanostructured composite fabricated by mechanical alloying

Production of bulk Al-TiB₂ nanocomposite from mechanically alloyed powder was studied. Al-20 wt.% TiB₂ metal matrix nanocomposite powder was obtained by mechanical alloying (MA) of pure Ti, B and Al powder mixture. A double step process was used to prevent the formation of undesirable phases like Al₃Ti intermetallic compound, which has been described in our previous papers. The resultant powder was consolidated by spark plasma sintering (SPS) followed up by hot extrusion. The structural characteristics of powder particles and sintered samples were studied by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Hardness measurements were conducted on the cross section of powder particles and sintered sample and the tensile behavior of extruded samples was evaluated. The results showed that the prepared Al-20 wt.% TiB₂ nanocomposite has good thermal stability against grain growth and particle coarsening. Extruded Al-20 wt.% TiB₂ showed a hardness value of 180 VHN and yield and tensile strength of 480 and 540 MPa, respectively, which are much higher than those reported for similar composites made by other processes.     

Microstructure and some properties of aluminium alloy AA6061 reinforced in situ formed zirconium diboride particulate stir cast composite

The objective of this work is to fabricate aluminium alloy AA6061 reinforced with ZrB₂ particles (10 wt-%) by the in situ reaction of K₂ZrF₆ and KBF₄ salts with molten aluminium. The microstructure, tensile strength, wear resistance and corrosion rate of the fabricated composite were compared with those of matrix alloy. The in situ formed ZrB₂ particles were uniformly dispersed in the aluminium matrix predominantly concentrated in inter granular regions and refined the microstructure of the matrix alloy. The incorporation of in situ formed ZrB₂ particles into the aluminium matrix improved tensile strength and wear resistance but reduced ductility and corrosion resistance.     

铝合金表面MoS2/Al2O3复合涂层制备及减摩性能研究

铝合金表面减摩涂层设计和制备是改善铝合金构件摩擦性能的关键技术之一。对于目前铝合金结构件易磨损的问题,本研究采用微弧氧化一步法在6063铝合金表面原位合成纳米MoS2,制备具有减摩作用的MoS2/Al2O3复合陶瓷涂层;讨论了硫盐浓度对涂层成分、形貌及摩擦性能的影响,分析了涂层减摩机理。结果表明：通过微弧氧化在6063铝合金表面成功制备出了含有MoS2的自润滑复合陶瓷涂层;涂层的摩擦系数随着硫盐浓度的升高呈现先下降后上升的趋势,当电解液中硫盐浓度为15g/L时涂层的摩擦系数为0.15,较常规微弧氧化涂层降低了76%。涂层中的MoS2分布在涂层的表面和内部,在与摩擦副接触与挤压的作用下形成均匀分布的MoS2润滑膜,表现出良好的减摩性能。     

Effects of trace TiB2 on microstructure in cast titanium alloys

Abstract

Effects of trace TiB₂ on solidification microstructure of Ti–6Al–4V alloy were investigated. The result shows that the microstructure of the ingot was refined by the added TiB₂. The grain size and α lath size were reduced gradually with the increase in TiB₂. The grain size is reduced by about an order of magnitude with an addition of 0·96 wt-%TiB₂, and the dendrite appears in the ingot. Such a tendency is similar to the change of the microstructure with boron addition. Ti–6Al–4V–B phase diagram and growth restriction factor Q are applied to analyse the influence mechanism of trace TiB₂ on the microstructure.     

Microstructure ofin situ MoSi2/SiC nanocomposite coating formed on Mo substrate by displacement reaction

The microstructure of an in-situ Mosi₂/β-SiC nanocomposite coating formed by the solid-state displacement reactions of Si deposited by chemical vapor deposition (CVD) with Mo-carbide layers at 1100°C, which had previously been formed on the surface of a Mo substrate by a CVD process, was investigated. The Mo-carbide layers formed by the simultaneous CVD of Mo and carbon at 900°C for 5 h using a gas mixture of C₂H₄−MoCl₅−Ar consisted of two layers, an inner layer of Mo₂C and an outer layer of MoC. While the monolithic MoSi₂ coating showed a typical colummar microstructure perpendicular to the Mo substrate, the MoSi₂/β-SiC nanocomposite coating formed by the solid-state displacement reactions between the Mo-carbide layers and Si was composed of equiaxed MoSi₂ grains with an average size of 150–500 nm and β-SiC particles with an average size of 80–105 nm. The β-SiC particles exhibited an oblate-spheroidal shape and were located mostly at the grain boundaries of MoSi₂. The volume percentage of β-SiC particles ranged from 18.5 to 29.2% with respect to the carbon concentration in Mo-carbide layers.     

Fabrication of Al alloys reinforced with AlN particles formed byin-situ reaction

The tensile properties and microstructures of Al alloys reinforced with AlN particles formed byin-situ reaction under a nitrogen atmosphere were analyzed. It was found that AlN particle layers formed on the surface of the Al particles in the powder bed, which replaced the Mg₃N₂ coated layers through the reaction, Mg₃N₂+2A1 → 2AlN+3Mg. The tensile strength and 0.2% offset yield strength in the control alloys were significantly greater than those in commercial alloys. This increase was due to the fine AlN particles formed by the abovein-situ reactions of the Mg₃N₂ formation and its decomposition into AlN. This article is based on a presentation made in the symposium “The l^st KIM-JIM Joint Symposium: High Strength Ratio Aluminum Alloys”, held at Inha University, Inchon, Korea, October 22, 1999 under the auspices of The Korean Institute of Metals and Materials and The Japanese Institute of Metals.     

The thermal stability in air of hot-pressed diboride matrix composites for uses at ultra-high temperatures

The resistance to oxidation in ambient air at a temperature up to 1600 °C of two hot-pressed diborides matrix composites, both containing 19.5% v/o SiC and 3 v/o HfN (as sintering aid), was investigated. The diboride matrix was based on HfB₂ or a ZrB₂/HfB₂ mixture (volume ratio ≈ 1). Both the materials were subjected to repeated heating-cooling cycles at 1600 °C, and a 20 h exposure at 1450 °C in flowing dry air. Modest weight gains and limited corrosion depths highlighted a rather good thermal stability. In accordance with the thermo-gravimetric test at 1450 °C, the oxidation kinetics for both the composites superbly fit a para-linear law. The introduction of the SiC particles provided tangible benefits for the resistance to oxidation. One of the oxidation products, a borosilicate glass, sealed pores and coated the exposed faces, greatly limiting the inward transport of oxygen towards the internal oxide/diboride interfaces.     

In situ investigation of SnAgCu solder alloy microstructure

In situ X-ray diffraction experiments, using synchrotron radiation, were employed to analyze microstructure evolution of the 96.5Sn3Ag0.5Cu (wt.%)—SAC305 lead-free solder alloy during heating (30-240 °C), isothermal dwell (240 °C) and cooling (240-30 °C). The special emphasis was placed on the study of the melting and solidification processes, explaining formation, distribution and the order of crystallization of the crystal phases (β-Sn, intermetallic compounds) in the solder alloy. Furthermore, thermal expansion behaviour of the main constituent phase β-Sn was analyzed prior to melting and after the consequent solidification.     

Face milling of the EN AB-43300 aluminum alloy by PVD- and CVD-coated cemented carbide inserts

Two commercially available WC-6Co cemented carbide substrates (Extramet EMT100 and Pramet H10), were industrially coated with PVD TiB₂ or CVD diamond. Subsequently, the coated inserts were submitted to dry sliding tests (slider on cylinder contact geometry) against the aluminum alloy EN AB-43300, for preliminary performance ranking and identification of basic wear mechanisms. The best substrate/coating combination (CVD-Diamond coated Extramet EMT100) was then tested in face milling EN AB-43300 with milling tool characterized by two different geometries (A and B), using PCD inserts as a reference for comparison. In milling tests, the influence of both insert geometry and cutting fluid feed rate were taken into account. The geometry of the tool was identified as the main parameter in influencing the tool performance. In particular, in the case of the A geometry, the relative flank wear of CVD coated tools increased abruptly during the test due coating detachment, whilst with the B geometry no catastrophic failure of the CVD coated insert was observed. The influence of Cutting Fluid Feed Rate (CFFR) also changed with tool geometry: in particular, with the B geometry, which allowed to obtain the best results with the CVD coated inserts, a decrease of CFFR from 100 to 25% did not affect significantly the wear resistance of CVD-coated inserts and allowed to maintain the roughness of the workpiece (R_a) below 0.6 μm, notwithstanding a slightly increased tendency towards the formation of Al-based transfer layers.     

Investigation of In situ Cu-TiB2 Composite on the Copper Using Laser Melting Synthesis

A surface composite layer reinforced with TiB₂ particles was produced on copper by use of the laser remelting in situ synthesis. The microstructure, electrical conductivity, and sliding wear behavior of the in situ Cu-TiB₂ composite were investigated. The experimental results show that the size of reinforcing TiB₂ particles is about 800 nm and the microhardness of composite layer reaches HV 210. Although the electrical conductivity of the composite layer is reduced with increasing TiB₂ volume fraction, the decrease of the integrated conductivity of the samples containing composite layer and copper substrate is insignificant. The wear resistance of composite layer is 10 times better than that of the copper sample.     

原位合成TiB2的定量计算及Cu-TiB2复合材料性能的研究

以Ti粉、B粉和Cu粉为原材料,球磨后,采用原位热压法合成Cu-15wt%TiB₂复合材料。详细讨论了Cu-Ti-B体系的反应过程。通过XRD、SEM、EDS、XPS等手段,确定了Ti和B在Cu基体中原位合成了TiB₂,并利用XRD制作TiB₂和Cu的定标曲线,采用外标法计算出不同烧结温度下TiB₂的合成率,结果表明,在一定的温度范围内,温度越高,合成率越高,在1000℃时TiB₂的合成率可达99.27%。并测试Cu-1.5 wt%TiB₂块状试样的维氏硬度,电导率和三点弯曲强度,分别为125.68 MPa、80.1% IACS和755.2 MPa,在100℃时的热膨胀系数和导热系数分别为9.3×10_-6 /K和260 W/mK。     

Mg-TiB2中间合金和Ca对AZ91D镁合金组织和性能的影响

采用SEM、EDS和XRD等测试手段,研究Mg-50%TiB2(质量分数)中间合金和碱土金属元素Ca对AZ91D镁合金组织和性能的影响。结果表明:0.7%TiB2和0.1%Ca可以显著细化AZ91D镁合金的枝晶组织和晶粒,α-Mg的平均晶粒尺寸由240μm下降至46μm。通过能谱分析及面错配度的计算证实:TiB2颗粒可作为初生α-Mg的良好异质形核核心。碱土金属元素Ca在晶界处富集,阻碍了α-Mg晶粒生长,对晶粒细化起到了一定的作用。显微组织的细化使合金的强韧性明显提高,并对耐腐蚀性能有较大改善。     

CuInSe2 nano-crystallite reaction kinetics using solid state reaction from Cu2Se and In2Se3 powders

The reaction mechanism and CuInSe₂ formation kinetics using a solid state reaction from Cu₂Se and In₂Se₃ powders synthesized using a heating up process were investigated using X-ray diffractomy (XRD) and transmission electron microscopy (TEM). It was observed that the CuInSe₂ phase increased gradually, accompanied with a decrease in γ-In₂Se₃ with no intermediate phase as the calcination temperature and soaking time were increased. The reaction kinetics was analyzed using the Avrami and polynomial kinetic model, suggesting that CuInSe₂ formation from Cu₂Se and In₂Se₃ powders follows a diffusion-controlled reaction with an apparent activation energy of about 122.5-182.3 kJ/mol. Cu₂Se and In₂Se₃ phases react and directly transform into CIS without the occurrence of any intermediate phase and the size of the newly formed CuInSe₂ crystallites was close to that of the Cu₂Se reactant particle based on the TEM results, which indicated that the solid reaction kinetics may be dominated by the diffusion of In³⁺ ions.     

Investigation on synthesis, pressureless sintering and hot pressing of chromium diboride

Experimental investigations were carried out on synthesis of chromium diboride through boron carbide reduction of Cr₂O₃. The products obtained were characterized by X-ray diffraction and the process optimized to prepare single-phase CrB₂ powder. Densification of CrB₂ was investigated by pressureless sintering and hot pressing. A maximum of 93% ρ_th was obtained by pressureless sintering at 1850 °C after a prolonged duration of 360 min. However, near theoretical density was achieved by hot pressing at 1600 °C and 35 MPa pressure for 2 h. The hardness and fracture toughness of fully dense CrB₂ was measured as 22 GPa and 3.5 MPa m^1/2, respectively. The mode of fracture in pressureless sintered samples is intergranular whereas that in hot pressed is transgranular.     

SiO2增加铝合金交流A-TIG焊熔深的机理

采用单组元活性剂进行铝合金交流A-TIG(Activating flux TIG)焊时,SiO2增加熔深最明显,对其增加熔深的机理进行了研究.进行正散焦真空电子束焊试验,SiO2对焊缝成形几乎没有影响;进行系列直流正接A-TIG焊试验,研究了活性剂对电弧的影响,发现SiO2使得氧化膜厚度增加,电弧极性区收缩,弧柱区扩展,电弧电压升高;进行氦气保护交流A-TIG焊试验,发现SiO2使活性剂或金属蒸发的区域变窄且蒸发量变小,熔池表面凹陷,并且在焊接过程中SiO2涂层始终存在于熔池表面,只在熔池凹陷中央区域出现很窄的裂缝,蒸气主要集中在电弧中下部.认为电弧极性区收缩和热输入增加是SiO2增加铝合金交流A-TIG焊熔深的主要机理.     

Structural evolution of mechanically alloyed Al-12Si/TiB2/h-BN composite powder coating by atmospheric plasma spraying

In the present study, mechanically alloyed Al-12Si/TiB₂/h-BN composite powder was deposited onto an aluminum substrate by atmospheric plasma spraying. The effect of mechanical alloying (MA) and plasma spray parameters on composite powder and coating structure were investigated. It has been observed that the MA process has a significant effect on the composite powder morphology and reactivity between the selective powders. Results also demonstrate that, at relatively high milling time h-BN decomposes into B and N and forms a solid solution. Also, it has been found that, the relative amount of the in-situ formed AlN through the reaction between h-BN and Al and/or the decomposition of Al-B-N solid solution is independent from the plasma parameters (arc current and secondary gas flow rate). However, spray parameters remarkably affects the coating hardness due to coarsening of Si during the solidification of the coating.