Effect of nucleating agent on the crystallization of tailings glass ceramics prepared by one-time sintering

Glass ceramics was made by the one-time sintering method using the main raw material of iron tailings. On the basis of quaternary system of CaO-MgO-Al₂O₃-SiO₂, using DTA, XRD and SEM, the effects of different nucleating agents and mixing amounts as well as heat treatment on the crystallization of tailings glass ceramics were studied. The experimental results show that, nucleating agent and heat treatment are two necessary conditions for one-time sintering preparation of tailings glass ceramics namely, only adding nucleating agent or experiencing heat treatment, the quaternary system can not crystallize. The composite nucleating agent consisting of Cr₂O₃ and TiO₂ can further lead to the crystallization of the CaO-MgO-Al₂O₃-SiO₂ quaternary system at the lower temperature, with the major phase of diopside. In the range of mass content, 0%–4%, crystal intensity and crystal content grow. But when mass content is more than 4%, the crystal size will become coarser and the crystal distribution will be less regular. Different heat treatment regimes do not change the composition of the crystalline major phase in the glass ceramics crystallization of CaO-MgO-Al₂O₃-SiO₂ system. In the range of 30–60 minutes, with the extension of nucleation and crystallization, crystallization degree enhanced, but if the holding time surpasses 60 minutes, the crystallization is worse. Funded by The National Key Technology R & D Program of China for the 11^th Five-Year Plan(2006BAJ04A04)     

Phase,magnetism and thermal conductivity of glass ceramics from iron ore tailings

In order to develop the applications of ore tailings, the glass ceramics were prepared by using a conventional melting-quenching-sintering process. The phase component, microstructures, magnetic properties and thermal conductivities of the prepared glass ceramics were investigated by using X-ray diffractometer, scanning electron microscopy, vibrating sample magnetometer and thermophysical properties tester, respectively. The results show that orthorhombic olivine-type phase and triclinic sunstone-type phase formed when the glass was annealed at 700 oC, the concentration of olivine-type and sunstone-type phases decreased, the spinel-type cubic phase occurred and the amount increased when the annealing temperatures increased. The magnetic properties from the cubic spinel ferrites were detected in the glass ceramics, and the related saturation magnetization increased with the annealing temperature increasing. The porous glass ceramics with magnetic property showed much lower thermal conductivity, compared with the non-magnetic porous glass-ceramic and the dense glass-ceramics.     

Effect of heat treatment on the mechanical properties of FeCoZrWB bulk metallic glass

A Fe61Co10Zr5W4B20 bulk metallic glass (BMG) with a diameter of 2 mm was prepared by using copper mould suction casting. The X-ray diffraction (XRD), differential scanning calorimetry (DSC), micro-hardness and compression tests were adopted to investigate the structure, thermal stability, especially, the effect of heat treatment on the micro-hardness and compression strength of this BMG. The BMG exhibits micro-hardness of about 1 207 Hv and compression fracture strength of about 1 707.6 MPa. After being annealed below the onset of crystallization temperature, the micro-hardness almost keeps constant. But after being annealed above the peak of crystallization temperature, the micro-hardness increases firstly and then declines gradually with the elongation of annealing time. However, annealed for the same period of time, the micro-hardness will increase with the rise of annealing temperature, while the compression fracture strength will apparently decrease.     

热处理温度对铟锡氧化物纳米粉显微结构的影响

采用化学共沉淀法制备了铟锡氢氧化物纳米粉，对其热处理前后的粉体进行了XRD和TEM分析，结果表明：未热处理的为铟锡氢氧化物，200℃热处理后铟锡氢氧化物部分晶化，300℃热处理后全部转变成晶态，然后随着温度升高逐渐转变为具有立方结构的铟锡氧化物纳米粉；600℃热处理1h后粉末粒度为5－10nm，铟锡质量比接近9：1。铟锡氧化物颗粒接近球形，分散性好。     

热处理工艺对高铬白口铸铁组织和性能的影响

分析了铸态及不同热处理工艺条件下高铬白口铸铁的组织和性能,结果表明：高铬白口铸铁铸态组织中共晶碳化物呈宫续和断续网状分布,对材料的韧性损害较大,通过热处理后可改善共晶碳化物的形态及分布,同时使基体组织到强韧化配合。     

Study on crystallization and microstructure of Li2O-Al2O3-SiO2 glass ceramics

Lithium aluminosilicate （LAS） glasses are generally difficult to prepare because of their high melting temperature. In this study, the preparation of LAS glasses was achieved at a relatively low melting temperature. The batch containing MgO-ZnO-LiEO- Al2O3-SiO2 was melted in a platinum crucible at 1550℃ for 2 h and was then followed by two- or three-step heat treatment processes for nucleation and crystal growth. The characterizations were carried out by differential thermal analysis, X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and UV-Vis-NIR scanning spectrophotometry. The hexagonal stuffed β-eucryptite solid solution crystallized at 840-960℃. Most of the hexagonal β-eucryptite solid solution transformed into the tetragonal β-spodumene solid solution at 1100℃. Almost all the aluminum atoms entered into the tetrahedral sites in the aluminosilicate network of the 6- eucryptite/β-quartz solid solution. All of the Al atoms did not belong to the aluminosilicate network of the β-spodumene solid solution. The glass ceramic with a mean grain size of 10-20 nm is transparent, the transmittance reaches -85% in the visible light wavelength.     

热处理对S7钢组织和硬度的影响

研究了热处理工艺对S7钢组织和硬度的影响,结果表明,S7钢在810－830℃加热,15－30℃/h冷却,软经效果最好,在850－880℃加热淬火,550℃回火,可满足热作模具钢的使用性能要求。     

Effects of heat treatment on microstructure and mechanical properties of Fe-Co-Ni-Cr-Mo-C alloy

A kind of Fe-Co-Ni-Cr-Mo-C alloy was designed for valve seat use. The effects of the quenching temperature, tempering time and tempering temperature on the mechanical properties and microstructure of the alloy were investigated. The results show that the hardness decreases, while tensile strength (σb), transverse rupture strength (σbb) and impact toughness(Kit) increase after the alloy is quenched and tempered. The best complex property (σb, 446 MPa; σbb ,793 MPa; Kic, 2.96 J/cm2 ) can be obtained when the alloy is quenched at 1 100 ℃ and tempered at 650 ℃. The results of X-ray diffraction and energy dispersive X-ray analysis (EDX) show that the major strengthening phases are carbides such as (Fe, Cr)7 C3 and Fe2 MoC. The obvious secondary hardening appears when the alloy is tempered at 550 ℃, which results from the precipitated carbides of Cr and Mo in the alloy from the matrix and the heat-resistant retained austenite .     

热处理对Cr26型高铬铸铁组织与性能的影响

研究Cr26型高铬铸铁经过不同的热处理后,其组织、硬度和耐磨性之间的关系。实验结果表明,最佳的淬火工艺是1 050℃×60 min后空冷,硬度为64.2 HRC;材料的硬度越高耐磨性能越好;并从组织状态和磨损机理方面分析了其原因。     

热处理工艺对27SiMn钢组织及力学性能的影响

为得到热处理工艺对27SiMn钢显微组织及力学性能的影响,制定了9种热处理工艺,并对其进行显微组织观察和力学性能测试.实验结果表明,27SiMn钢淬火＋回火后的显微组织与回火温度和时间有关,当回火温度低、时间短时,显微组织为回火屈氏体＋马氏体;当回火温度高、时间长时,显微组织为回火屈氏体＋回火索氏体.同时,回火温度和时间对27SiMn钢的力学性能有很大影响,当回火温度为450℃,时间为45 min时力学性能最高,抗拉强度为1 175 MPa。当热处理温度为490℃,时间为75 min时力学性能最差,抗拉强度为975 MPa.综合分析27SiMn钢热处理最优工艺为900℃淬火＋475℃回火75 min。     

4Cr5MoSiV1热处理工艺及组织的研究

研究了显象管玻壳模具用 4Cr5MoSiV1钢的不同热处理工艺下的组织与硬度的关系 ,特别是回火温度与硬度的关系 ,提出了预备热处理采用 1 1 0 0℃淬火 ,82 0℃回火的调质处理替代退火处理 ,随后经 1 0 2 0℃淬火 ,780～80 0℃× 4h回火 2次 ,并改善炉内温度分布状况 ,可得到较为均匀理想的组织和性能     

Effects of heat treatment on the microstructure and mechanical properties of ZA84 magnesium alloy

The effects of heat treatment on the microstructure and mechanical properties of ZA84 (Mg-8Zn-4Al-0.25Mn) alloy were investigated. The results indicate that the as-cast microstructure of the alloy is mainly composed of α-Mg matrix and two different morphologies of precipitates (continuous and quasi-continuous Mg32(Al,Zn)49 phases and isolated Mg5Al2Zn2 phases). After solid solution treatment at 345°C, the Mg32(Al,Zn)49 phases change from continuous and quasi-continuous net to disconnected acute angle shape,...     

热处理对反向挤压AZ80镁合金组织与性能的影响

采用光学和扫描电子显微观察、X射线衍射及拉伸试验研究了反向挤压AZ80镁合金不同热处理状态下的显微组织及性能．结果表明：反向挤压AZ80镁合金热处理后析出的β－Mg17Al12相（β相）在不同热处理状态下形貌不同．经T6热处理后,口相在晶界处呈层片状析出,与挤压态相比,合金的强度稍有降低,但延伸率明显提高;经T5热处理后,卢相在晶界处仍呈层片状,而在晶内呈颗粒状,与挤压态相比,合金的强度明显提高,但延伸率降低．     

溶胶-凝胶法制备BST/MgO复合陶瓷的结构研究

采用溶胶-凝胶法制备了未掺杂和掺Mg的钛酸锶钡的干凝胶和陶瓷。经DSC/TG、XRD以及SEM研究观察表明:BST干凝胶在500℃开始晶化,700℃晶化完全。BST/MgO陶瓷的烧结温度为1 300℃。在1 300℃烧结后,陶瓷中只有钙钛矿一个相,不含有任何杂相,说明了Mg2+完全进入了晶格,并且取代的是B位离子Ti4+。随着MgO掺杂含量的增加,BST/MgO陶瓷的晶粒先得到细化,而后开始增大,气孔率不断降低。     

热处理对ITO薄膜的显微结构及光电特性的影响

以硝酸铟和四氯化锡为源材料,无水乙醇和乙酰丙酮为溶剂,采用溶胶—凝胶工艺制备出纳米晶ITO透明导电薄膜.采用XRD和SEM分析了薄膜的物相和显微形貌,采用面电阻测量仪和分光光度计测量了薄膜的方阻和可见光透过率.实验结果表明,随着热处理温度升高,晶化程度提高,组织逐渐均匀致密,晶粒长大,700℃热处理时薄膜晶化趋于完善.同时,方阻减小而可见光透过率增加.经过700℃热处理、厚度为400nm的ITO膜的方阻约300Ω/□,可见光透过率>80%.     

A New Technology of Microcrystallizing Leucite to Reinforce Dental Glass Ceramics

The key technology and the main mechanism of microcrystallizing leucite to reinforce dental glass ceramics were investigated. The feedstock powders were selected, mixed according to the ratios of the theoretical composition of leucite, ball - milled, melted at 1600℃ and then cooled to room temperature quickly. The cooled clinkers were troll - milled again to 4μm. After cold - isostatic pressure molded and air sintered at 1500℃ for 1 h, the dental glass ceramics were fabricated. They have following characteristics : excellent mechanical properties (mean compressive strength is 206.6 MPa ), low sintering temperature and good reoccurrence to keep steady quality.     

Effect of cyclic heat treatment on microstructure and mechanical properties of 50CrV4 steel

An annealed 50 Cr V4 steel was subjected to cyclic heat treatment process that consists of repeated short-duration(200 s)held at 840 °C(above Ac3 temperature of 790 °C) and short-duration(100 s) held at 700 °C(below Ac1 temperature of 710 °C). The spheroidization ratio of cementite and the average size of particles increase with increasing the cyclic number of heat treatment. After5-cycle heat treatment, the spheroidization ratio of cementite is 100%, and the average size of the cementite particles is about0.53 μm. After cyclic heat treatment, the hardness, ultimate tensile strength and yield strength of the experimental steel gradually decrease with increasing cyclic number of heat treatment. The elongation of the as-received specimens is about 7.4%, the elongation of the 1-cycle specimen is 14.3%, and the elongation of 5-cycle specimen reaches a peak value of 22.5%, thereafter marginally decreases to 18.3% after 6-cycle heat treatment. Accordingly, the fractured surface initially exhibits the regions of wavy lamellar fracture. By increasing the cyclic number of heat treatment cycles, the regions of dimples consume the entire fractured surface gradually. Some large dimples can be found in the fracture surface of the specimen subjected to six heat treatment cycles.     

真空热处理对热障涂层组织形貌及元素扩散的影响

为了研究真空热处理对CoNiCrAlY涂层组织形貌及元素扩散的影响,采用超音速火焰喷涂(HVOF)设备在镍基高温合金基体上制备了CoNiCrAlY涂层.对部分样品进行真空热处理,利用大气等离子喷涂8YSZ陶瓷层.采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、能谱分散谱仪(EDS)等分析了热障涂层的相组成、微观组织、元素扩散与热震性能,研究了真空热处理对热障涂层的影响.结果表明,真空热处理后,CoNiCrAlY涂层颗粒间界面消失且涂层发生均质化;涂层与基体界面处元素发生扩散;热障涂层的抗热震性能提高.