【作者】 王东；

【导师】 王玉金；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2018， 博士

【摘要】 采用Zr-Cu二元熔体作为浸渗剂,IV–VIB族碳化物为多孔坯体,低温反应熔渗制备了组织和性能良好的反应自生ZrC-Cu基复合材料。相比IVB和VB族碳化物反应熔渗制备反应自生ZrC-MeC-Cu复合材料的过程,Zr-Cu熔体与VIB族Mo和W碳化物的反应较缓和,容易控制。制备的ZrC-Mo-Cu和ZrC-W-Cu复合材料组织均匀。相比W+WC和WC坯体,采用部分碳化的W粉制备的ZrC-W-Cu复合材料具有无WC残余、组织均匀、反应时间短的优点。坯体预烧可以使材料性能稳定。冷等静压100 MPa获得孔隙率47.0–53.6%的多孔坯体,在1300℃反应熔渗Zr₂Cu熔体1h后得到了W含量48–73vol%的ZrC-W-Cu复合材料。ZrC_x-TiC_y-Cu、内晶型ZrC-TiC/W-Cu、ZrC_x-NbC_y-Cu、ZrC_x-TaC_y-Cu以及ZrC-Mo-Cu复合材料的显微组织沿浸渗方向出现分层现象。Zr含量增加时,反应、传质速度明显加快,复合材料晶粒粗大;Zr含量低,反应缓和,材料组织均匀。复合材料中生成的富W纳米颗粒及层状纳米相、Ta₂C、Nb₂C等板状晶通过偏转、桥连裂纹能够有效提高复合材料的断裂韧性。ZrC_x-TiC_y-Cu、内晶型ZrC-TiC/W-Cu、ZrC_x-NbC_y-Cu和ZrC_x-TaC_y-Cu复合材料的断裂韧性分别达到9.67±0.96、10.21±0.31、12.1±4.4和5.34±1.70 MPa·m^1/2。ZrC-Mo-Cu复合材料的抗弯强度和断裂韧性分别达到569 MPa和8.2 MPa·m^1/2。ZrC-W-Cu材料由W、ZrC和晶间富Cu相组成,基本没有WC残余。ZrC晶内存在金属（W、Cu）及金属间化合物（W₃Cu、Cu₅Zr）纳米相。当W含量从73vol%降低到48vol%时,ZrC-W-Cu复合材料的显微硬度从4.71 GPa升高到8.93 GPa,抗弯强度从519 MPa增大到657 MPa,断裂韧性由9.1 MPa·m^1/2提高到10.6MPa·m^1/2。在氧乙炔焰下烧蚀60–120s后,ZrC-73vol%W-Cu复合材料的线烧蚀率和质量烧蚀率仅0.8μm·s^-1和3.5mg·s^-1。当材料中W含量小于50vol%时,材料容易发生热震破坏。材料的耐烧蚀机理主要是形成了粘稠ZrO₂保护层和WO₃、Cu的发汗冷却。利用W和Mo物理、化学性质相似的原理,采用Mo作为指示剂,通过分析(W_0.9Mo_0.1)C固溶体和Zr-Cu熔体反应界面的元素分布、物相和组织揭示了Zr-Cu熔体和WC固体反应的规律。(W_0.9Mo_0.1)C致密块体和多孔预制体分别在1200–1600℃和Zr-Cu熔体反应15 min后,W、Mo元素发生偏聚。在Zr-Cu熔体和ZrC晶粒内部发现W偏聚区。表明固熔反应时存在WC向Zr-Cu熔体中溶解的过程。随着反应温度的升高、熔体中Zr含量的增加以及WC颗粒尺寸的降低,溶解速度和溶解量增大。当Zr-Cu熔体中Zr的活度低于0.3时,溶解的W以单质形式析出;当Zr含量较高时,以W-Zr金属间化合物形式析出;当反应温度超过1600℃时,反应界面形成连续ZrC层阻隔WC和熔体的接触,后续反应受C原子在ZrC/W产物层中的扩散控制。1300℃时,用Zr₂Cu/WC（Zr/C=1）混合粉末制备的ZrC-W-Cu复合材料中,反应时间从10 min延长到60 min,a _ZrC由0.4665 nm增大到0.4671 nm。W、Cu原子的固溶使a _ZrC减小。W、Cu原子在有C空位的ZrC晶格内固溶时,结构的形成能较低;溶解度随C空位浓度减小而降低。ZrC晶粒内的富Cu/W纳米相的形成机理是:Cu/W在ZrC_x中的固溶度随C空位浓度减小而降低;随时间延长,反应初期固溶的Cu/W原子以金属单质或金属间化合物形式析出。更多还原

【Abstract】 The prepared self-generated ZrC-Cu based composites were prepared by reactive melt infiltration at relatively low tempwerature.The Zr-Cu binary melt was used as the infiltrant and the IV-VIB carbide was the porous preforms.Compared with ZrC-MeC-Cu composite from IVB and VB carbides,the reaction of Zr-Cu melt with VIB Mo and W carbides is mild and easy to control.The as-prepared ZrC-Mo-Cu and ZrC-W-Cu composites have uniform microstructure.Compared with W+WC and WC preformss,ZrC-W-Cu composites prepared by partially carbonized W powder have the advantages of no WC residue,uniform structure and short reaction time.The calcination of the green body can stabilize the material properties.A porous preform with a porosity of 47.0–53.6%was obtained by cold isostatic pressing at 100 MPa.ZrC-W-Cu composite with a W content of 48–73 vol%was obtained after 1 h of Zr2Cu melt at 1300℃.The microstructure of ZrCx-TiCy-Cu,intragranular ZrC-TiC/W-Cu,ZrCx-NbCy-Cu,ZrCx-TaCy-Cu and ZrC-Mo-Cu composites showed delamination along the infiltration direction.When the Zr content increased,the reaction and mass transfer rate are obviously accelerated,the composite grains are coarse;when the Zr content is low,the reaction is moderate,and the material structure is uniform.The W-rich nanoparticles and layered nano-phases,Ta2C,Nb2C and other plate-like crystals formed in the composite material can effectively improve the fracture toughness of the composite by deflection and bridging cracks.The fracture toughness of ZrCx-TiCy-Cu,intragranular ZrC-TiC/W-Cu,ZrCx-NbCy-Cu and ZrCx-TaCy-Cu composites reached 9.67±0.96,10.21±0.31,12.1±4.4 and 5.34±1.70 MPa·m^1/2,respectively.The flexural strength and fracture toughness of ZrC-Mo-Cu composites reached 569 MPa and 8.2 MPa·m^1/2,respectively.The ZrC-W-Cu material consists of W,ZrC and intercrystalline Cu-rich phases,with substantially no WC residue.There are metal（W,Cu）and intermetallic（W3Cu,Cu5Zr）nano phases in the ZrC grain.When the W content is reduced from 73vol%to48vol%,the microhardness of ZrC-W-Cu composite increases from 4.71 GPa to 8.93GPa,the flexural strength increases from 519 MPa to 657 MPa,and the fracture toughness increases to 9.1 MPa·m^1/2 to 10.6 MPa·m^1/2.The linaer ablation rate and mass ablation rate of ZrC-73vol%W-Cu composites were only 0.8μm·s^-1 and3.5mg·s^-11 after ablation for 60–120 s under oxyacetylene flame.When the W content in the material is less than 50 vol%,the material is prone to thermal shock damage.The ablation resistance of the material is mainly the formation of a viscous ZrO2protective layer and the sweating cooling of WO3 and Cu.Using Mo as an indicator,Zr-Cu was revealed by analyzing the element distribution,phase and microstructure of the（W0.9Mo0.1）C solid solution and Zr-Cu melt reaction interface.The law of the reaction between the melt and the WC solid.（W0.9Mo0.1）C dense and bulk pre-formed at 1200–1600℃ and Zr-Cu melt reaction for 15 min,respectively,W,Mo elements are segregated.A W segregation zone was found inside the Zr-Cu melt and ZrC grains.It indicates the presence of WC dissolution into the Zr-Cu melt during the solid solution reaction.As the reaction temperature increases,the Zr content in the melt increases,and the WC particle size decreases,the dissolution rate and the amount of dissolution increase.When the activity of Zr in the Zr-Cu melt is less than 0.3,the dissolved W precipitates as a simple substance;when the Zr content is high,it precipitates as a W-Zr intermetallic compound;when the reaction temperature exceeds 1600℃,The reaction interface forms a continuous ZrC layer to block the contact of the WC with the melt,and subsequent reactions are controlled by the diffusion of C atoms in the ZrC/W product layer.The segregations of W and Mo elements in the Zr-Cu melts and W rich inclusions in ZrC grains after reaction show both W and C in WC solid both dissolve into the Zr-Cu melts at the initial contact of the melt and WC solid.The dissolution rate and amount of W and C increase with decreasing radius of the WC particles and increasing Zr content in the Zr-Cu melts and the reaction temperature.The nucleation rate and growth rate both improve a lot with raising temperature.The dissolution of WC is restrained by the formation of a continuous ZrC layer,when the reaction temperature is 1600℃.However,there is always a dissolution process of WC causing incorporation of W atoms into Zr-Cu melt in the initial contact between the melt and solid.At 1300℃,the ZrC-W-Cu composite prepared by Zr2Cu/WC（Zr/C=1）mixed powder extended the reaction time from 10 min to 60 min,and a ZrC increased from0.4665 nm to 0.4671 nm.The solid solution of W and Cu atoms reduces aZrC.When the W and Cu atoms are dissolved in the ZrC lattice with C vacancies,the formation energy of the structure is low;the solubility decreases with the decrease of the C vacancy concentration.The formation mechanism of Cu/W-rich nanophase in ZrC grains is:the solid solubility of Cu/W in ZrCx decreases with the decrease of C vacancy concentration;with the extension of time,the solid solutes of Cu/W atoms precipitate in the form of elemental or intermetallic compounds.更多还原