Influence of Adding Ti Powder in Preform on Microstructure and Mechanical Properties of Al_2O_3p/Steel Composites by Squeeze Casting

To improve the mechanical properties of alumina particulates reinforced steel matrix composite, Ti powder was added into the alumina preform, a 5140 steel matrix composite was fabricated by squeeze casting, and the influences of Ti powder on the microstructure, hardness and bending strength of the composite were investigated, compared with the composite without adding Ti powder. Applied Ti powder and alumina particulates were 10-25 μm and 100-180 μm in size, respectively. Both composites were successfully fabricated, however Ti powder addition increased the infiltration thickness of the composite. In the Ti contained composite, a TiC film in micron scale is formed on the surface of alumina particles, many TiC aggregates are dispersed in the steel matrix without obvious remaining Ti powder. The hardness and the three-point bending strength of the composite reach 49.5 HRC and 1 018 MPa, respectively, which are 17.9% and 52.4% higher than those of the composite in the absence of Ti addition. Fracture morphology shows that the debonding of alumina particulates is eliminated for the composite in the presence of Ti addition. Sessile drop test shows the average wetting angle between 5140 steel and that of Ti coated Al2O3 is about 82.15°, much lower than the wetting angle 150° between steel and pure Al2O3. Therefore, the increase in the mechanical properties of the composite is attributed to the improvement of Al2O3 p/steel interface wetting and bonding by adding Ti powder in the preform.

Synergistically Toughening Effect of SiC Whiskers and Nanoparticles in Al_2O_3-based Composite Ceramic Cutting Tool Material

In recent decades, many additives with different characteristics have been applied to strengthen and toughen Al2O3-based ceramic cutting tool materials. Among them, SiC whiskers and SiC nanoparticles showed excellent performance in improving the material properties. While no attempts have been made to add SiC whiskers and SiC nanoparticles together into the ceramic matrix and the synergistically toughening effects of them have not been studied. An Al2O3-SiCw-SiC np advanced ceramic cutting tool material is fabricated by adding both one-dimensional SiC whiskers and zero-dimensional SiC nanoparticles into the Al2O3 matrix with an effective dispersing and mixing process. The composites with 25 vol% SiC whiskers and 25 vol% SiC nanoparticles alone are also investegated for comparison purposes. Results show that the Al2O3-SiCw-SiCnp composite with both 20 vo1% SiC whiskers and 5 vol% SiC nanoparticles additives have much improved mechanical properties. The flexural strength of Al2O3-SiCw-SiCnp is 730＋ 95 MPa and fracture toughness is 5.6 ± 0.6 MPa.m1/2. The toughening and strengthening mechanisms of SiC whiskers and nanoparticles are studied when they are added either individually or in combination. It is indicated that when SiC whiskers and nanoparticles are added together, the grains are further refined and homogenized, so that the microstructure and fracture mode ratio is modified. The SiC nanoparticles are found helpful to enhance the toughening effects of the SiC whiskers. The proposed research helps to enrich the types of ceramic cutting tool and is benefit to expand the application range of ceramic cutting tool.

Al2_3/Al2O3 Joint Brazed with Al2O3-particulate-contained Composite Ag-Cu-Ti Filler Material

Microstructure and interracial reactions of Al2O3 joints brazed with Al2O3-particulate-contained composite Ag-Cu-Ti filler material were researched by scanning electron microscopy （SEM）, electron probe microscopy analysis （EPMA）, energy dispersive spectroscopy （EDS） and X-ray diffraction （XRD）. The interracial reaction layer thickness of joints brazed with conventional active filler metal and active composite filler materials with different volume fraction of Al2O3 particulate was also studied. The experimental results indicated although there were Al2O3 particulates added into active filler metals, the time dependence of interracial layer growth of joints brazed with active composite filler material is t^1/2 as described by Fickian law as the joints brazed with conventional active filler metal.

Ti/Al_2O_3 Functionally Gradient Material Prepared by the Explosive Compaction/SHS Process

Ti1Al2O3 Functionally Gradient Material (FGM) was prepared by an explosive compaction/SHS process. Ten sheets of the compounding powder were laminated and pressed to get a green body of FGM. It was then compacted explosively By burying the explosive compaction body into a stoichiometric Al/TiO2 mixture and igniting the combustion of the stoichiometric Al/TiO2 mixture, the SHS reaction of the explosive compaction body was initiated by the heat released from the combustion of the stoichiometric Al/TiO2 mixture. In this way, Ti/Al2O3 FGM was synthesized. The adiabatic temperatures of each gradient layer were calculated when the preheating temperatures were 298 K and 1173 K, respectively The microstructure, composition and properties of Ti/Al2O3 FGM and the reaction mechanism of each gradient layer were studied. It was found that Ti/Al2O3 FGM prepared by the explosive compaction/SHS process had a high density and a high microhardness. Its structure, composition and properties showed apparent gradient distribution. The structure of the standard stoichiometric ratio gradient layer of FGM was a network structure. Its reaction mode could be described as follows: Al powder melted first, then the molten Al penetrated into the TiO2 zone and reacted with TiO2, and big pores were left in the original positions of Al powder. The reaction of gradient layers with the addition of Al3O3 as diluents was similar to that of the standard stoichiometric ratio gradient layer, so were their structure and composition. However, the reaction of gradient layers with the addition of Ti as diluents was more complex and the composition deviated slightly from the designed one

SiO_2微粉加入量对Al_2O_3-SiC-C出铁沟浇注料性能的影响

采用高铝矾土(8～5 mm)、棕刚玉(8～5、5～3、3～1 mm)、SiC(≤1、≤0.044 mm)、致密刚玉(≤1、≤0.044 mm)为主要原料,固定SiO2微粉和白泥的总加入量(w)为2.5%,研究了SiO2微粉加入量(其质量分数0、1%、1.5%、2%、2.5%)对Al2O3-SiC-C浇注料性能的影响。结果表明:试样在1 100、1 500℃分别保温3 h处理后,随着SiO2微粉加入量的增加即白泥加入量的降低,其加热永久线变化逐渐减少,显气孔率呈现先增大后降低的趋势,体积密度的变化趋势与显气孔率的正好相反,常温抗折强度及高温(1 450℃0.5 h)抗折强度呈现先增大后降低的趋势;当SiO2微粉加入量(w)为1.5%时,试样热震后的残余强度最大,SiO2微粉加入量(w)为2%的试样的强度保持率最低;在SiO2微粉加入量(w)为2%时,材料的抗渣侵蚀性能最好,继续增大SiO2微粉含量,抗渣侵蚀性能下降。综合各方面的因素,SiO2微粉和白泥复合使用时,SiO2微粉加入量(w)为2%左右,白泥加入量(w)为0.5%左右时,Al2O3-SiC-C快干浇注料具有最佳的综合性能。根据试验结果制备的快干浇注料在莱钢750 m3单铁口高炉铁沟使用,在未经任何修补的情况,主沟一次通铁量达到14万t。

氮化硅铁在Al_2O_3-SiC-C质铁沟浇注料中的防氧化行为

将Al_2O_3-SiC-C系铁沟浇注料及分别添加 8% (质量分数)氮化硅、氮化硅铁的浇注料试样在空气中进行 1500℃ 3h热处理后,分别对氧化层进行形貌(SEM)及能谱分析(EDS),并结合热力学分析了氮化硅铁的防氧化行为:高温氧化气氛下,表面氮化硅铁中的Si3N4首先氧化生成SiO2,构成氧化层的主体;随着铁相材料的氧化,形成的氧化铁不但降低了氧化层的熔点,而且降低了熔体的粘度,增进熔体在材料表面上的润湿性及流动性,形成覆盖于材料表面的氧化层而阻止碳素氧化,使其具有比纯氮化硅更好的防氧化性能;另外,由于氮化硅铁在Al2O3 -SiC-C系材料中加入量少,而且试样内部的铁不是以氧化铁形式存在的,故对材料高温使用性能的影响不大。

改性石墨对Al_2O_3-SiC-C质铁沟浇注料性能的影响

为了解决鳞片石墨因密度小、润湿性差和分散困难而难以在浇注料中使用的问题,首先采用硅烷偶联剂KH-560对≤0.178和≤0.074 mm的鳞片石墨分别进行改性处理,得到两种粒度的改性石墨;然后在传统Al2O3-SiC-C质铁沟浇注料配方(w):电熔致密刚玉62%、SiC粉24%、α-Al2O3微粉5%、纯铝酸钙水泥4%、SiO2微粉3%、球状沥青(≤1 mm)2%的基础上,分别用0.5%(w)的改性前后的石墨等量取代球状沥青,以研究KH-560硅烷偶联剂改性鳞片石墨对Al2O3-SiC-C铁沟浇注料性能的影响。结果表明:与原石墨相比,改性后石墨的分散性明显改善,浇注料的需水量大幅降低,且加入≤0.178 mm改性石墨的试样分散效果较好;含石墨试样的常温物理性能均有所下降,但加入≤0.178 mm改性石墨的试样强度和体积密度都明显高于加入其他石墨的,仅略低于无石墨的;加入石墨的试样抗渣性能明显得到提高,且加入≤0.178 mm改性石墨试样的抗渣性能最佳。综合考虑浇注料的各项性能,认为经硅烷偶联剂改性的鳞片石墨可部分取代球状沥青,且最佳粒度为≤0.178 mm。

原位生成SiAlON增强Al_2O_3-SiC-C铁沟浇注料的力学性能

根据热力学计算 ,在还原气氛下 ,通过引入Si3N4 和提高Si的加入量等途径原位合成制备出SiAlON增强Al2 O3-SiC -C浇注料是完全可行的。实验研究了Si3N4 的加入量和Si的加入量对Al2 O3-SiC-C铁沟浇注料力学性能的影响。结果发现 :随着Si3N4 加入量的提高 ,材料的力学性能先增大 ,后减小 ,加入量为 6 %时材料力学性能最佳 ;Si的加入量对材料性能的影响较为显著 ,材料的力学性能随着其加入量的增多而逐渐提高 ,其最佳加入量为 5 %。XRD及SEM分析结果表明 ,SiAlON增强Al2 O3-SiC -C铁沟浇注料性能优良的根本原因是由于Si3N4 、Si与Al2 O3原位反应生成的SiAlON改变了材料基质结合形式 ,提高了基质的固

矾土骨料对Al_2O_3-SiC-C铁沟浇注料性能的影响

为降低铁沟浇注料的原料成本,以粒度>1 mm的高铝矾土熟料GL-90和矾土均化料GL-88分别替代常规棕刚玉质Al2O3-SiC-C铁沟浇注料中>1 mm的棕刚玉颗粒,研究了这两种不同矾土骨料对铁沟浇注料的影响。结果表明:不同矾土骨料对铁沟浇注料的流动性、体积密度、强度以及抗渣侵蚀性均有不同程度的影响。相对矾土均化料而言,品位较高的高铝矾土熟料更适合作为铁沟浇注料中棕刚玉的替代品,以其为主要骨料制成的铁沟浇注料,其各项性能指标与以常规棕刚玉质铁沟浇注料的更为接近,而且在铁水温度不高、热冲击较小的中小型高炉上,这种铁沟浇注料与棕刚玉质铁沟浇注料的使用效果差别不大;而在铁水温度较高、热冲击大的高炉上,与棕刚玉质的使用效果差别较大,尤其是在撇渣器前端回旋区,应尽量使用棕刚玉质的铁沟浇注料。

蓝晶石对硅溶胶结合Al_2O_3-SiC-C浇注料性能的影响

为了提高Al2O3-Si C-C浇注料在高温使用过程中的体积稳定性,用蓝晶石粉部分替代Al2O3-Si C-C浇注料中的白刚玉粉,研究了蓝晶石加入量(质量分数分别为0、1%、2%、3%、4%、5%和6%)对浇注料经烘干和1 400℃保温3 h热处理后物理性能的影响。结果表明:随着蓝晶石加入量的增加,试样经1 400℃保温3 h热处理后由微收缩逐渐变为微膨胀,体积稳定性以蓝晶石加入量为5%(w)时为最好。经110℃烘24 h后试样的显气孔率、常温耐压强度和常温抗折强度变化都很小,体积密度基本上呈降低趋势;经1 400℃保温3 h热处理后试样的显气孔率基本上呈先升高后降低的变化趋势,体积密度则呈相反的变化趋势,并且均以蓝晶石加入量3%(w)为拐点;常温耐压强度和常温抗折强度略有降低,但降低幅度很小。同一配比的试样,1 400℃保温3 h热处理后的体积密度、显气孔率、常温耐压强度、常温抗折强度均比经110℃烘24 h后的高。XRD、SEM和EDS分析表明,蓝晶石发生了一次莫来石化反应而产生体积膨胀,有效缓解了试样的烧结收缩,使试样具有较好的体积稳定性。

硅粉对硅溶胶结合Al_2O_3-SiC-C浇注料性能的影响

以特级矾土熟料（5～3、3～1 mm）、棕刚玉（≤1 mm）、SiC（≤1 mm）、球状沥青（1～0．5 mm）、电熔白刚玉（≤0．074 mm）、活性α-Al2O3微粉、SiO2微粉、硅粉（d50＝20．81μm）为原料制备Al2O3-SiC-C浇注料，分别以质量分数为0、1％、2％、3％、4％、5％和6％的硅粉等量替代白刚玉粉，研究了硅粉对浇注料常温物理性能和抗氧化性能的影响，并采用Factsage、SEM和EPMA等手段对试样进行热力学分析和显微结构分析。结果表明：1）随着硅粉含量的增加，试样的显气孔率逐渐降低，体积密度先增大后减小，常温强度明显提高。2）硅粉可以提高浇注料的抗氧化性能，在硅粉加入量为4％（w）时，其抗氧化性能最好。3）抗氧化试验后，试样边缘部位原位反应生成的莫来石堵塞了气孔，使得试样边缘结构致密；试样过渡区域有少量的莫来石和SiO2生成，封闭了表面的气孔，进一步阻止了氧气的进入；试样中心区域有少量晶须状的SiC生成，填充在骨架结构中，起强化增韧的作用。

氮化硅-氧氮化硅复合粉对Al2O3-SiC-C铁沟料性能的影响

为了进一步提高Al 2O3-SiC-C出铁沟浇注料的性能并降低其生产成本,在其中加入质量分数分别为0、2%、4%、6%、8%的氮化硅-氧氮化硅复合粉等量替代其中的碳化硅粉,加水搅拌均匀后,检测料浆的流动性,再经浇注成型、养护、烘干、不同温度(800、1100和1450℃)热处理等程序制成浇注料试样,然后检测浇注料试样的线变化率、显气孔率、体积密度、常温抗折强度、热态抗折强度和抗渣性,并采用XRD分析浇注料试样的物相组成。结果表明:1、加入氮化硅-氧氮化硅复合粉后,Al 2O3-SiC-C出铁沟浇注料的初始流动值减小,烧后线变化率、显气孔率、体积密度、常温抗折强度和热态抗折强度变化不大,抗高炉渣侵蚀性提高。2、综合考虑,氮化硅-氧氮化硅复合粉的最佳加入量为4%(w)。

SiAlON增强Al_2O_3-SiC-C铁沟料用后分析

对原位SiAlON增强Al2O3-SiC-C铁沟浇注料进行了工业应用试验,并对用后铁沟浇注料残样进行了XRD、SEM和EMPA分析。结果表明:1)SiAlON增强Al2O3-SiC-C铁沟浇注料抗侵蚀性优良,一次性通铁量达到15万t以上;2)用后SiAlON增强Al2O3-SiC-C铁沟浇注料可分为蚀变层、反应层和原质层,各层中均有粒状β-SiAlON分布;3)SiAlON增强Al2O3-SiC-C铁沟浇注料在现场使用环境下比在实验室条件下更容易原位生成β-SiAlON,β-SiAlON的生成是该浇注料具有优良使用性能的根本原因。

硅溶胶结合Al_2O_3-SiC-C浇注料的抗侵蚀性能

以致密刚玉、碳化硅、炭素材料、氧化铝微粉、刚玉微粉等为原料,以硅溶胶为结合剂制备了Al2O3-SiC-C浇注料,与高炉出铁场应用的主沟铁线料、渣线料以及脱Si用摆动流嘴料对比进行了抗高炉水渣、脱Si渣和脱P渣侵蚀试验研究,侵蚀试验采用静态坩埚法(氧化气氛,1450℃3h)和动态旋转法(1500℃,转速为60r.min-1,试验旋转时间10min)两种方法进行。另外,对所研制的浇注料又进行了静态坩埚强化侵蚀试验:1500℃3h抗渣侵蚀试验和2次1450℃3h抗渣侵蚀试验。结果表明:所研制的硅溶胶结合Al2O3-SiC-C浇注料对3种渣的抗侵蚀性能均比目前高炉出铁场使用的主沟铁线料、渣线料以及脱Si用摆动流嘴料要好;在3种铁水预处理渣中,脱Si渣和脱P渣对材料的侵蚀较严重。

结合剂对Al2O3-SiC-C质铁沟浇注料性能的影响

研究了铝酸钙水泥、铝酸钙水泥/SiO2微粉、-αAl2O3微粉以及-αAl2O3微粉/SiO2微粉4种结合剂对Al2O3-SiC-C质浇注料性能的影响。结果表明,加入-αAl2O3微粉结合剂的材料性能最好,可以获得性能良好的铁沟浇注料。

改性石墨对Al2O3-SiC-C质浇注料性能的影响

以传统Al2O3-SiC-C质浇注料的基本配方为基础,制备成沥青质量分数为2%的Al2O3-SiC-C质浇注料和改性石墨质量分数分别为2%、4%和6%的Al2O3-SiC-C质浇注料,对比研究了这几种浇注料的流动性及经110℃、1 100℃和1 500℃处理后浇注体的体积密度、体积稳定性、强度、抗氧化性和抗渣性。结果表明:随着碳源由沥青改为改性石墨以及随着改性石墨加入量的增多,浇注料的需水量增多;不同温度处理后浇注体的体积密度均先增后降;烘干后强度降低较多,烧后强度变化相对较小;抗氧化性差别不大;高温抗折强度明显提高;添加改性石墨的浇注料比添加等量沥青的抗渣性差,但随着改性石墨加入量的逐渐增多,其抗渣性又有所提高。

高炉出铁沟用Al_2O_3-SiC-C质浇注料的研究进展

介绍了Al2O3、SiC和碳3种主要原料在Al2O3-SiC-C质浇注料中的作用,详细综述了不同氧化物及非氧化物添加物、结合剂、粒度分布及分散剂对其性能的影响及机理,分析了Al2O3-SiC-C质浇注料未来的发展趋势,并提出了将来可能的研究方向。

硅铝凝胶粉结合SiAlON增强A1_2O_3-SiC-C浇注料

以电熔致密刚玉和碳化硅为骨料,硅铝凝胶粉、氮化硅粉、硅粉为细粉,制成SiAlON增强Al2O3-SiC-C浇注料,研究了硅铝凝胶粉的加入量分别为1%、3%、5%(质量分数,下同)时对此浇注料的烧结性能、力学性能的影响。结果表明:采用硅铝凝胶粉取代纯铝酸钙水泥作结合剂,可使SiAlON增强Al2O3-SiC-C浇注料在经中温、高温热处理后的常温抗折强度及耐压强度较大提高,中温、高温强度提高幅度更大。另外,随着硅铝凝胶粉加入量的增加,浇注料的常温及高温强度呈先增大而后减小的趋势。由X射线衍射和扫描电镜分析结果可知,硅铝凝胶粉的加入既有利于降低βSiAlON的生成温度,又可以减少材料中的低熔物质。分布均匀、发育良好的粒状βSiAlON的形成是SiAlON增强Al2O3-SiC-C浇注料较水泥结合浇注料强度高的根本原因。

高纯二氧化硅微粉含量对Al_2O_3-SiC-C铁沟渣线浇注料性能的影响

以棕刚玉颗粒(15～8 mm,8～5 mm,5～3 mm,3～1 mm),板状烧结刚玉(1～0 mm),碳化硅(3～1 mm,≤1 mm,≤0. 063 mm)、白刚玉粉,活性氧化铝微粉和高纯二氧化硅微粉以及单质硅粉和球状沥青等为主要原料,制备了出铁沟渣线用Al_2O_3-SiC-C质浇注料,并研究了高纯硅微粉含量对其流动性及高温使用性能的影响。结果表明:随高纯硅微粉含量的增加,浇注料的初始流动性基本呈增加趋势,且其流动值的保持时间延长。随高纯硅微粉含量的增加,浇注料的热态抗折强度呈增加趋势,且抗侵蚀性也会增强。

废Al_2O_3-SiC-C砖在铁沟浇注料中的回收利用

为了开发废Al2O3-SiC-C砖的回收利用,以废Al2O3-SiC-C砖颗粒作为骨料取代高铝均化料,制备了一系列废Al2O3-SiC-C砖不同掺入量(质量分数25%、40%和55%)的铁沟浇注料。从试验检测结果和现场使用效果两方面对废Al2O3-SiC-C砖颗粒取代高铝均化料的可行性进行了对比分析,并从经济效益和社会效益两方面对废Al2O3-SiC-C砖的回收利用进行了综合评估。结果表明:随着废Al2O3-SiC-C砖掺入量的提高,浇注料的需水量逐渐增多,体积密度逐渐降低,烧后线变化率逐渐减小,强度略有降低但仍保持着较高水平,抗渣侵蚀性能未受明显影响;与原浇注料相比,掺入质量分数为40%的废Al2O3-SiC-C砖颗粒的浇注料在中小型高炉出铁场支沟及渣沟上的使用效果差别较小,寿命降低不明显,而原材料成本可大幅降低;另外,由于对废Al2O3-SiC-C砖进行了回收再利用,减少了大量固体废弃物堆砌造成的资源浪费与环境破坏,因此产生了显著的社会效益。