【作者】 刘利盟；

【导师】 周玉； 叶枫；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2007， 博士

【摘要】 采用溶胶-凝胶法合成了BaAl₂Si₂O₈ （BAS）及Ba_0.75Sr_0.25Al₂Si₂O₈ （BSAS）非晶粉末,通过DSC非等温结晶动力学及1450℃等温结晶试验,揭示了Sr²⁺对钡长石玻璃粉末的结晶行为及其六方→单斜相变的影响规律。采用热压烧结法合成了50wt%Si₃N₄/BSAS陶瓷材料,XRD物相及热膨胀分析表明单斜钡长石仅能与α相Si₃N₄共存,β-Si₃N₄使得六方钡长石更加稳定。以氧化物原位反应生成BAS或BSAS玻璃陶瓷为基础,采用放电等离子烧结法（1800℃/5min）和无压烧结法（1900℃/60min）合成了70wt%Si₃N₄增强BAS及BSAS陶瓷材料,并进行（1800℃/60min/2.0MPaN2）后续热处理;采用热压烧结法1800℃/80min和1700℃/40min+1800℃/120min合成了70wt%Si₃N₄/BAS和60wt%Si₃N₄/BAS陶瓷材料。系统研究了烧结方式、烧结工艺及热处理对显微组织及力学性能的影响规律。结果表明:（1）热压和SPS法与无压烧结法相比可促进液相润湿Si₃N₄,从而提高Si₃N₄的转变速率;（2） SPS烧结不但能够实现Si₃N₄/BAS和Si₃N₄/BSAS陶瓷材料的快速致密化,还能够完成Si₃N₄/BAS陶瓷材料中Si₃N₄的α→β转变;（3） SPS结合后续热处理或两步烧结法,避免致密化过程中Si₃N₄的α→β转变,利用原料中混入β-Si₃N₄晶粒的成核作用,可在Si₃N₄/BAS陶瓷材料中产生双模式组织;（4）经过热处理调整显微结构并缓解残余应力,材料的弯曲强度和断裂韧性可达968 MPa和8.9 MPa·m1/2,断口为穿晶断裂,棒晶传递并承受载荷、裂纹桥连和偏转是主要的强韧化机制。以10wt%BAS作添加剂,采用热压烧结法（1800℃/80min）合成了高韧性的复相（10%α+90%β）-SiAlON和（40%α+60%β）-SiAlON陶瓷材料。显微组织的特征为高长径比β-SiAlON棒晶均匀分布在α-SiAlON及BAS共同构成的基体上。晶间相BAS有利于界面脱开及裂纹偏转、棒晶桥连,使复相（α+β）-SiAlON/BAS陶瓷材料具有较高的弯曲强度和断裂韧性。以5wt%BAS作添加剂,采用热压烧结法合成了化学式为RE_1/3Si₁₀Al₂ON₁₅的自韧化α-SiAlON/BAS陶瓷材料,系统地研究了烧结工艺、后续热处理、稀土类型（单元和双元）对自韧化α-SiAlON/BAS陶瓷材料的物相、显微组织演变及力学性能的影响规律。阐述了中间相β-SiAlON出现的原因,并采用控制烧结工艺参数及高温热处理两种方法予以消除;采用1200℃/2h-1500℃/1h-1800℃/1h三步烧结法排除BAS溶解RE、Al、N等因素的影响,促进α-SiAlON的形成,获得了理想相组成的α-SiAlON/BAS（5wt%）陶瓷材料;BAS液相能够显著改变α-SiAlON晶粒的生长行为,提高α-SiAlON陶瓷材料中棒晶的含量及其长径比,有效地实现了α-SiAlON/BAS （5wt%）陶瓷材料的自韧化。这种新型陶瓷材料的显微组织及力学性能可通过改变稀土类型及可控热处理等方法进行优化。BAS溶解少量的稀土元素可促进钡长石结晶及六方→单斜相转变。更多还原

【Abstract】 Amorphous BaAl₂Si₂O₈ （BAS） and Ba_0.75Sr_0.25Al₂Si₂O₈ （BSAS） powders were synthesized by a sol-gel process. The effect of Sr on the non-isothermal crystallization kinetics and hexacelsian to celsian phase transformation were studied by DSC and heating at 1450℃for 30min to 210min. Si₃N₄ reinforced BAS/BSAS composites were hot-pressed, using the sol-gel BAS, BSAS, andα-Si₃N₄ as starting powders. Phase compatibility research results suggested that hexacelsian was stabilized by the presence ofβ-Si₃N₄, and consequently the desired celsian phase was unobtainable in the Si₃N₄/BAS system.Si₃N₄ reinforced BAS/BSAS glass ceramic matrix composites of optimal compositions were synthesized by spark plasma sintering （SPS, 1800℃/5min）, pressureless sintering （PLS, 1900℃/60min）, and hot pressing （HP1, 1800℃/80min, and HP2, 1700℃/40min+1800℃/120min）, using oxides as the BAS/BSAS precursors. Post heat-treatment at 1800℃for 60 min in 2.0MPa nitrogen was held. The effects of the transient liquid, sintering techniques, and heat-treatment, on the microstructure and thereof the mechanical performances of the composites was elucidated. The results indicated that （1） SPS and HP increased theα→β-Si₃N₄ phase transformation rate because of the promoted wetibility by the external pressure in comparison to PLS; （2） In case of SPS, Si₃N₄/BAS and Si₃N₄/BSAS composites were densified rapidly within 5min during sintering, butα→β-Si₃N₄ phase transformation was completed only in the Si₃N₄/BAS system; （3） By manipulating the grain growth driving force through a two-step hot-pressing or through the combination of SPS with heat-treatment, the abnormal growth of theβ-Si₃N₄ nuclei in the starting powders resulted in a bimodal microstructure, hence enhancement of mechanical properties; （4） When microstructure optimization and thermal mismatch stress release were achieved by controlled heat-treatment, high flexure strength and fracture toughness could reach 968MPa and 8.9MPam1/2 respectively. Load transfer, bridging, and crack deflection were the main reinforcing mechanisms revealed by fracture SEM observation.Dual-phase （α+β）-SiAlON with 10wt% and 40wt%α-SiAlON were obtained using 10wt% BAS as additives via hot pressing. Elongatedβ-SiAlON grains with large aspect ratio over 10 dispersing homogeneously in the BAS andα-SiAlON matrix was the microstructure feature of the composites. BAS intergranular phase benefited the interfacial debonding, crack deflection, pull-out, and bridging of the largeβ-SiAlON grains, imparting high toughness to the materials.Self-reinforcedα-SiAlON ceramics of RE_1/3Si₁₀Al₂ON₁₅ composition with 5wt% BAS additive were fabricated using hot-pressing. The effects of sintering parameters, post heat-treatment, types of rare-earths and dual-rare-earth dopants on the phase assemblage development were systemically manifested. The presence of metastableβ-SiAlON and its elimination by means of sintering process control and post sintering heat-treatment were established. The successful application of the three-step sintering of 1200℃/2h-1500℃/1h-1800℃/1h to elude the dissolve of rare earth, and AlN into the BAS liquid yieldedα-SiAlON/BAS（5wt%） ceramics of ideal phase constituents. High aspect ratio ofα-SiAlON grains from the elongated growth which was secured by the steady BAS liquid during sintering, guaranteed the self-reinforcing of the composites. Microstructure and mechanical properties could be further improved by tailoring the rare-earth dopants and the sintering-heat treatment procedures. Small amount of rare-earth dissolving in the BAS accelerated its crystallization and the hexacelsian to celsian phase transformation, which should have positive effects on the high temperature strength of the SiAlON.更多还原