Thermodynamic Analysis of the Formation of In-situ Reinforced Phases In Cast AI-4.5Cu Alloy

The thermodynamic analysis of the formation of in-situ reinforced phases in (TiB2 Al3Ti)/Al-4.5Cu composites prepared by mixed salts reaction was conducted, and heat changes of mixed salts system were analyzed by differential thermal analysis (DTA). The results show that although TiB2 possesses the strongest formation ability in Al-Ti-B ternary system, [Ti] is relatively excessive in the in-situ reaction and it combines with Al to form Al3Ti phase. The reinforced phases are TiB2 and Al3Ti in the produced composites due to the reaction taking place to form reinforced phase with the addition of mixed salts into Al-4.5Cu melt between 900℃ and 1032℃.     

High-temperature oxidation behavior of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiAl matrix composite in air

The oxidation behavior of Al₂O₃/TiAl in situ composites fabricated by hot-pressing technology was investigated at 900° in static air. The results indicate that the mass gains of the composites samples decrease gradually with increasing Nb₂O₅ content and the inert Al₂O₃ dispersoids effectively increase the oxidation resistance of the composites. The higher the Al₂O₃ dispersoids content, the more pronounced the effect. The primary oxidation precesses obey approximately the linear laws, and the cyclic oxidation precesses follow the parabolic laws. The oxidized sample containing Ti₂AlN and TiAl phases in the scales exhibits excellent oxidation resistance. The oxide scale formed after exposure at 900°C for 120 h is multiple-layered, consisting mainly of an outer TiO₂ layer, an intermediate Al₂O₃ layer, and an inner TiO₂+Al₂O₃ mixed layer. From the outer layer to the inner layer, TiO₂+Al₂O₃ mixed layer presents the transit of Al-rich oxide to Ti-rich oxide mixed layer. Near the substrate, cross-section micrograph shows a relatively loose layer, and micro- and macro-pores remain on this layer, which is a transition layer and transferres from Al₂O₃+TiO₂ scale to substrate. The thickness of oxide layer is about 20 μm. It is also found that continuous protective alumina scales can not be observed on the surface of oxidation scales. Ti ions diffuse outwardly to form the outer TiO₂ layer, while oxygen ions transport inwardly to form the inner TiO₂+Al₂O₃ mixed layer. Under long-time intensive oxidation exposure, the internal Al₂O₃ scale has a good adhesiveness with the outer TiO₂ scale. No obvious spallation of the oxide scales occurs. The increased oxidation resistance by the presence of in situ Al₂O₃ particulates is attributed to the enhanced alumina-forming tendency and thin and dense scale formation. Al₂O₃ particulates enhance the potential barrier of Ti ions from M/MO interface to O/MO interface, thereby the TiO₂ growth rate decreases, which is also beneficial to improve the oxidation resistance. Moreover, the multi-structure of the TiO₂+Al₂O₃ mixed layer decreases the indiffusion of oxygen ions and also avails to improve the high temperature oxidation resistance of the as-sintered composites. Supported by the Special Program for Education Bureau of Shaanxi Province, China (Grant No. 08JK240) and Scientific Research Startup Program for Introduced Talents of Shaanxi University of Technology, China (Grant No. SLGQD0751)     

Synthesis of Ti3SiC2/TiB2 Composite by In-situ Hot Pressing （HP） Method

Ti3SiC2/TiB2 composite was successfully obtained by hot pressing Ti/TiC/Si/B4C power mixtures.Volume fraction of TiB2 in Ti3SiC2/TiB2 composite can not exceed 10%.Incorporation of excessive TiB2 will affect the reactions process.TiC and Ti5Si3 were two important intermediate phases during the whole reactions.The microstructure characteristics of the Ti3SiC2/TiB2 composites were analyzed using scanning electron microscopy （SEM） and transmission electron microscopy （TEM）.The experimental results show that the grains of Ti3SiC2/TiB2 composite are structured in a layered form,and the formation of TiB2 particles as reinforcements with elongated or equiaxed shape distributes in Ti3SiC2 matrix.     

Effect of matrix composition on physical properties of Al<Subscript>3</Subscript>CON in-situ reaction reinforced corundum composite

60% white corundum used for aggregate, 5% aluminium powder for fixed additions and 35% various additives for matrix were prepared for specimens 1#,2#,3#. They were mixed uniformly with the suitable resin as a binder and pressed under pressure of 315 ton forging press, then dried at 200℃ for 24 h. Effects of various additives on 1500 ℃×2 h creep properties of Al3CON reinforced corundum composite were researched. The experimenal results show that creep coefficients of specimens 1#,2#,3# at 1500 ℃×2 h are 1.4×10^- 4, -9.4×10^-4, -22.6×10^-4, respectively. Crushing strength of the slide plate added with suitable additive A after fired at 1500 ℃ ×3 h reaches to 225 MPa, the creep rate is positive all the time from 0% to 0.014% at 1500 ℃ for 2 h. The microstructure result analysis shows that reinforced phases of Al3CON fiber composite have been formed after fired with Al powder in coke at high temperatures for specimen 1#, and the strength of the composite is increased. The hot modulus of rupture is up to 59 MPa at 1400 ℃ and the RUL is obviously higher than that at 1700 ℃. Its service life is two times as that of Al2O3-C slide plate when used in the process of pouring steel. The mechanism of creep rate resistance of the composites can be discovered by means of SEM and EDAX analysis. It is concluded that the active Al3CON and Al2O3 multiphases that were formed by N2 in gas, C, Al and Al2O3 inside the matrix of the composites during in-situ reaction,which gives the composites outstanding creep rate resistance for the dense zone resuiting from Al3CON oxidation that inhibits contraction at the high temperature. Besides, the matrix will turn into the multiphase with high refractoriness, N content and its Al3CON reinforced fiber will further increase accordingly. In addition, Al3CON formed by Al2O3 and C, Al in the matrix with N2 in gas will inhibit the creep rate and also greatly improve the creep rate resistance of the composites.     

Self-Propagating High-Temperature Reduetive Synthesis of TiB2-Al2O3 Composite Powders

TiB2-Al2O3 composite powders were produced by self-propagating high-temperature synthesis（SHS） method with reductive process from B2O3-TiO2-AI system. X-ray diffraction（XRD） and scanning electron microscopy（SEM） analyses show the presence of TiB2 and Al2O3 only in the composite powders produced by SHS. The powders are uniform and free-agglomerate. Transmission electron microscopy （TEM） and high resolution electron microscopy （HREM） observation of microstructure of the composite powders indicate that the interfaces of the TiB2-Al2O3 bond well, without any interfacial reaction products. It is proposed that the good interfacial bonding of the composite powders can be resulted from the TiB2 particles crystallizing and growing on the Al2O3 particles surface with surface defects acting as nucleation centers.     

In situ prepared Al-Si alloy matrix composites reinforced by γ-Al2O3p

A γ-Al2O3 particles reinforced Al-Si alloy matrix composite was fabricated by adding NH4Al（SO4）2 to molten aluminum alloy. TEM observation shows that in-situ γ-Al2O3 particles are generally spherical and uniformly distributed in the matrix. The results of dry sliding wear tests show that the wear resistance of the composites increases with increasing mass fraction, and the volume loss is considerably lesser than that of the matrix and is lesser than that of the composites by adding γ-Al2O3 particles directly.     

Microstructures and mechanism of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al composites fabricated by the reaction between SiO<Subscript>2</Subscript> and molten aluminum

Al₂ O₃/Al composite was fabricated by the reaction between SiO₂ and molten aluminum. The microstructures of the composite obtained under different reaction conditions were analyzed. The formation mechanism of the composite microstructure was discussed. Results show that the reaction kinetics is influenced remarkably by the reaction temperature, reaction time and the quantity of SiO₂. The morphologies of Al₂O₃ have different features, depending on the reaction temperature. The composite has equaxed Al₂O₃ grains when materials reacted below 1200°C, and the composite is composed of a large number of fine Al₂O₃ grains and aluninum. The composite has a frame-shaped Al₂O₃ microstructure at the reaction temperature of above 1250°C. CHENG Xiao-min: Born in 1964 Funded by the National Natural Science Foundation of China (No. 91522)     

Mechanism and kinetic model of <Emphasis Type="Italic">in-situ</Emphasis> TiB<Subscript>2</Subscript>/7055Al nanocomposites synthesized under high intensity ultrasonic field

In-situ TiB2/7055Al nanocomposites are fabricated by in situ melt chemical reaction from 7055Al-K2TiF6-KBF4 system under high intensity ultrasonic field,and the mechanism and kinetic model of in-situ melt chemical reaction are investigated.X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses indicate that the sizes of in-situ TiB2 nanoparticles are in the range of 80-120 nm.The results of ice-water quenched samples show that the whole process contains four stages,and the overall in-situ reaction time is 10 minutes.The in situ synthesis process is controlled mainly by chemical reaction in earlier stage (former 3 minutes),and by the particulate diffusing in later stage.The mechanism of key reaction between Al3Ti and AlB2 under high intensity ultrasonic in the 7055Al-K2TiF6-KBF4 system is the reaction-diffusion-crack-rediffusion.Furthermore,the reactive kinetic models in 7055Al-K2TiF6-KBF4 system are established.     

Thermodynamics and kinetics of in-situ formation of TiAl3/7075 composites

The thermodynamics and kinetics of the reaction between Titanium powder and 7075 aluminum alloy were investigated to assess the possibility of preparing TiAl₃/7075 composites by in-situ synthesis method. Results show that Ti and Al melt can form TiAl₃ spontaneously, which is considered as a reinforced phase of the matrix. Measurements such as XRD, SEM, and EDX were performed to characterize the as-synthesized samples, and results confirmed the formation of TiAl₃ in aluminum matrix composites. The reactive kinetics was controlled by three main factors, which are the system temperature, particle size of Ti, and the thickness of external diffusion layer.     

Effects of Ti,Al and Hf on niobium silcides formation in the Nb-Si <Emphasis Type="Italic">in situ</Emphasis> composites

The effects of alloying elements Ti, Al and Hf on niobium silicides formation in the Nb-Si in situ composites have been investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The binary, ternary and multicomponent alloys have been fabricated by vacuum non-consumable arc melting method. The results show that Ti tends to stabilize Nb₃Si phase, while Al promotes the direct formation of β-Nb₅Si₃ phase with a tetrahedral D8 _m structure. Exceptionally, it seems that Hf is beneficial to the formation of γ-Nb₅Si₃ phase with a hexangular D8₈ structure. For the multicomponent Nb-Si in situ composites, the cooperative effects of different elements on niobium silicides formation basically maintain the character of ternary system.     

复合活性钎料钎焊Cu与Al2O3的接头组织及性能

为改善紫铜与Al_2O_3陶瓷的连接强度,采用纳米-Al_2O_3增强的AgCuTi复合钎料(Ag Cu Tip)对紫铜与Al_2O_3陶瓷进行了真空钎焊.采用扫描电镜、能谱分析以及剪切试验对钎焊接头微观组织及力学性能进行了分析.钎焊接头典型界面组织为紫铜/扩散层/铜基固溶体+银基固溶体+Ti_2Cu+Ti_3(Cu,Al)3O/Al_2O_3.纳米-Al_2O_3的添加抑制了Al_2O_3侧反应层的生长,并促进钎缝中形成弥散分布的Ti_2Cu相.随着保温时间的延长,铜侧扩散层和Ti_3(Cu,Al)_3O反应层的厚度逐渐增大.保温时间为20 min时,铜母材向钎料过度溶解,降低了接头性能.当钎焊温度为880°C,保温10 min时,接头抗剪强度最高为82 MPa.纳米颗粒的加入细化了钎缝组织并降低了母材与钎缝热膨胀系数的不匹配,因此提高了接头的连接性能.保温时间可影响界面组织及反应层的厚度,进而影响接头的连接强度.     

Fabrication and magnetic properties of Sm3(Fe,Ti)29Nx/α-Fe dual-phase nanocomposite permanent magnetic material

Sm3(Fe,Ti)29Nx/α-Fe dual-phase nanometer magnetic material was fabricated through rapid solidification, crystallization and nitridation of Sm-Fe (Ti) alloy. The effect of combination of rapid solidification and Ti alloy addition on the phase formation and microstructure of the Sm-Fe alloy is investigated in this paper. The microstructure of amorphous phase and dual-phase nano-grain crystals before and after crystallization annealing were observed using a high-resolution transmission electron microscope (HREM). The dual-phase nano-grains after annealing were compacted together with a clear interface with the direct exchange-coupling mechanism. Different annealing processes were used to examine the melt-spun alloy. Comparison of the images of SEM showed that annealing at 750℃ for 10 min was most suitable to get homogeneous and nano-grains. No obvious kink was detected in the second quadrant of the hysteresis loop like a single hard magnet, and strong exchange coupling was found between hard magnets and soft magnets.     

Effect of Mg/Al ratios on hydration mechanism of tabular alumina carbon composites reinforced by Al<Subscript>4</Subscript>C<Subscript>3</Subscript> in situ reaction

Hydration mechanism of tabular alumina carbon composites reinforced by Al₄C₃ in situ reaction with Mg and Al was researched in water steam using super automatic thermostatic water bath from 25 °C to 85 °C. It is shown that hydration mechanism of the composites is chemical reaction control at 44.3 °C-84 °C in H₂O(g). The hydration was controlled by diffusion from 24.7 °C to 33 °C. The ratio of added Mg/Al influences the HMOR of the composites.The mechanism of HMOR of the composites with different ratios of Mg/Al can be discovered by means of SEM analysis. The active Mg/Al powder and flake graphite inside give the composites outstanding hot strength resulting from the interlocking structure of Al₄C₃ crystals at high temperature. Besides, the matrix changes into the Al₄C₃ with high refractoriness. The method of preventing the hydration of tabular alumina carbon composites reinforced by Al₄C₃ in situ reaction was immersed in the wax at suitable temperature or storing them below 33 °C in a dry place or storing them with paraffin-coating.     

The influence of mo additive on the microstructure and property of Ti/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite

The influence of Mo on the microstructure, bending strength and HV of Ti/Al₂O₃ composite was studied, and the influence mechanism was analyzed. The results indicate that after the addition of Mo, the composite organization is finer and phases distribution is better-proportioned which make the microstructure denser, the bending strength and HV of composite are also increased to a degree. But the bending strength increases first then decreases with the increasing of Mo content, so the appropriate Mo content for the Ti/Al₂O₃ composite is to be further confirmed. WANG Zhi: Born in 1962 Funded by Natural Science Foundation of China (No. 50232020) and Natural Science Foundation of Shandong Province (No. 2002F21)     

Microstructure and mechanical properties of TiB<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites

Effects of Al2O3 and Ni as the additives on the sinterability, microstructure and mechanical properties were systematic studied. The experimental results show that only a relative density about 96.2% of hot-pressing TiB2-30%Al2O3 can be attained due to the plate-like TiB2 particle and its random orientation and excessive Al2O3 grain growth. When sintering temperature is higher than 1 700 ℃, TiB2 grain growth can be found, which obvious improves flexural strength of TiB2 matrix but decreases toughness. It seems that mechanical properties of TiB2-Al2O3 composites are mainly depended on relative density besides grain growth. otherwise, they will be determined by relative density and TiB2 matrix strength together. Anyway, Al2O3 addition can weaken the grain boundary and thus improve the toughness of the materials. A flexural strength of 529 MPa, Vickers hardness of 24.8 GPa and indentation toughness of 4.56 MPa·m1/2 can be achieved inTiB2-30vol% Al2O3.     

Flux pinning effect of cubic equiaxed morphology and its Ti stabilizing in Nb<Subscript>3</Subscript>Sn superconductors

Two sets of internal-Sn Nb3Sn superconducting strands were fabricated through RRP method, one with 2 wt% of Ti alloyed in Sn core and the other just pure Sn. Four reaction temperatures of 650℃, 675℃, 700℃ and 725℃ and 128 h duration were applied for A15 phase formation heat treatment after Cu-Sn alloying procedure of 210℃/50 h + 340℃/25 h. For the heat-treated coil samples, transport non-Cu JC was examined through standard 4-probe technique and phase microstructure was observed by means of Field Emission Sc...     

Effect of TiB2 content on resistance to sodium penetration of TiB2／C cathode composites for aluminium electrolysis

TiB2/C cathode composites with various contents of TiB2 were prepared and their characterizations were observed and compared. The expansion of samples due to sodium and bath penetration was tested with a modified laboratory Rapoport apparatus and the appearances of the cut sections of specimens after electrolysis were studied.The results show that the mass of TiB2/C cathode composites with mass fraction of TiB2 less than 70% appreciably increases, but that of the composites with mass fraction of TiB2 more than 70% decreases slightly after being baked.The resistance to sodium and bath penetration of TiB2/C cathode composites increases with the increase of TiB2 content, especially in the composites with high TiB2 content. TiB2/C cathode composites have high resistance to the penetration of sodium and bath as well as good wettability by molten aluminum, and keep integrality and have little change of appearance after electrolysis, which indicates that TiB2/C cathode composites can be used as inert wettable cathode for aluminum electrolysis.     

Influence of TiX (<Emphasis Type="Italic">X</Emphasis>=B<Subscript>2</Subscript> or N) addition on the interfacial microstructure features of CBN grains and AgCuTi composite filler

Joining experiments of CBN grains to AISI 1045 steel were conducted using Ag-Cu-Ti composite fillers containing TiX (X=B₂ or N) particles at 920 °C for 5 min. The influences of TiB₂ and TiN particles on the interfacial microstructure features between CBN and filler were investigated comparatively. The experimental results show that TiN particles are more effective than TiB₂ ones to control the interfacial reaction and particularly the resultants. Thermodynamic analysis reveals that the varied interfacial reaction induced by the addition of TiB₂ and TiN particles is mainly atttributed to the activity change of the B and Ti elements in the brazing reaction system.     

Phase structure and electrical properties of La<Subscript>2</Subscript>O<Subscript>3</Subscript>-doped BiInO<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> ceramics with high curie temperature

The phase structure and electrical properties of pure and La2O3-doped Bi-InO3-PbTiO3 （BI-PT） ceramics were studied respectively. In （1 -x）BI-xPT （x=0.72-0.80） ceramics, the stability of tetragonal phase increased with increasing x, and pure perovskite structure was obtained for x=-0.80 ceramics. The phase transition temperature range was between 575 ℃ and 600 ℃ for x=0.72-0.80 ceramics, higher than that of PT （-490 ℃）. The c/a ratio almost linearly decreased with increasing La2O3 content in x-0.80 ceramics. It is believed that Pb^2＋ vacancies were formed by La^3＋ substituting Pb^2＋ in La2O3-doped BI-PT ceramics. Tc shifted to lower temperature by 30 ℃/mol% La2O3. The maximum dielectric constant 8557 around 559 ℃ was exhibited in 0.5mol%-doped BI-0.80PT ceramics. La2O3-doped ceramics could be poled resulting from decreasing of c/a ratio and improving of dielectric loss and resistivity. The maximum piezoelectric coefficient d33 was 12 pC/N for 2mol%-doped BI-0.80PT ceramics.     

Preparation of Al2O3-SiO2-TiO2-ZrO2 Composite Ceramic Membranes by Sol-Gel Method

Al2O3-SiO2- TiO2-ZrO2 supported membranes were prepared by Sol-Gel method. These composite ceramic membranes are level, even and no macro crack. There exist several crystalline phases such as Al2O3, TiO2 ( anatase ), Al2 SiO5 , and ZrO2 in these membranes. Changing the molar ratio of Al:Si: Ti : Zr ,the kinds and content of crystal phases of composite membranes could be different, which may lend to a variety of microstructure of membranes. The surface nanoscale topography and microstructure of membranes were investigated by XRD, SEM, AFM, EPMA. The effects of additives and heat treatments on the surface nanoscale topography and microstracture of composite ceramic membranes were also analyzed.