HfB2 is well-known as one of the Ultra-High Temperature Ceramics (UHTCs) have attracted attention and expected to have application in extreme environments because of the unique and excellent characteristics such as high melting point excess 3000 °C, distinguished thermo-mechanical properties, and chemical stability, while it is difficult to produce the UHTCs fabrication of large complex shape parts due to poor sinterability. Thus, for the practical use of UHTCs in complex structures, it will be required an effective method of joining, as partial transient liquid phase (PTLP) bonding that utilizes interfacial diffusion and reaction at liquid phase generated in multilayer interlayer, and enables junction preserves the adhesion and the heat resistance. The present study aimed at investigating the mechanical properties of HfB2 joints with different Ni/Nb/Ni interlayer thickness by four-point bending test at room temperature and at high temperature (1000 °C, under air). HfB2 based composite with MoSi2 as a sintering aid was fabricated by pressureless sintering method. The multilayer interlayer combinations were Sample A consisted of core layer Nb (=127 ?m) with cladding layer Ni (=2 ?m), and Sample B consisted of core layer Nb (=25.4 ?m) with cladding layer Ni (=0.4 ?m). Joining assemblies were hot-pressed at 1500 °C for 30 min under 20 Pa vacuum with a constant 8.5 MPa applied pressure, then the interfacial region of joint was systematically investigated by using EPMA and FESEM-EDS. The joints were four-point bending tested both at room and high temperature, and fractographic investigations were done. Cross-sectional FESEM images of joints with the results of compositional analyses were shown in Figure 1 and 2, respectively. It was found that the Ni/Nb/Ni interlayer of Sample B revealed more intensive interfacial reaction with HfB2 composite. Additionally, the bending strength of Sample A and Sample B at room temperature reached 412 ±53.9 MPa and 398 ±139 MPa respectively. Then at high temperature (1000 °C, under air), the bending strength of Sample A and Sample B reached 337 ±17.1 MPa and 187 ±132 MPa respectively. These results indicated that adequate thick Ni suppressed interfacial reaction between HfB2 composite and interlayer and enabled HfB2 joints reserved the better bending strength even at elevated temperature.
EFFECT OF Ni-Nb INTERLAYER THICKNESS ON MECHANICAL PROPERTY OF HfB2 COMPOSITE JOINTS
2015
Abstract
HfB2 is well-known as one of the Ultra-High Temperature Ceramics (UHTCs) have attracted attention and expected to have application in extreme environments because of the unique and excellent characteristics such as high melting point excess 3000 °C, distinguished thermo-mechanical properties, and chemical stability, while it is difficult to produce the UHTCs fabrication of large complex shape parts due to poor sinterability. Thus, for the practical use of UHTCs in complex structures, it will be required an effective method of joining, as partial transient liquid phase (PTLP) bonding that utilizes interfacial diffusion and reaction at liquid phase generated in multilayer interlayer, and enables junction preserves the adhesion and the heat resistance. The present study aimed at investigating the mechanical properties of HfB2 joints with different Ni/Nb/Ni interlayer thickness by four-point bending test at room temperature and at high temperature (1000 °C, under air). HfB2 based composite with MoSi2 as a sintering aid was fabricated by pressureless sintering method. The multilayer interlayer combinations were Sample A consisted of core layer Nb (=127 ?m) with cladding layer Ni (=2 ?m), and Sample B consisted of core layer Nb (=25.4 ?m) with cladding layer Ni (=0.4 ?m). Joining assemblies were hot-pressed at 1500 °C for 30 min under 20 Pa vacuum with a constant 8.5 MPa applied pressure, then the interfacial region of joint was systematically investigated by using EPMA and FESEM-EDS. The joints were four-point bending tested both at room and high temperature, and fractographic investigations were done. Cross-sectional FESEM images of joints with the results of compositional analyses were shown in Figure 1 and 2, respectively. It was found that the Ni/Nb/Ni interlayer of Sample B revealed more intensive interfacial reaction with HfB2 composite. Additionally, the bending strength of Sample A and Sample B at room temperature reached 412 ±53.9 MPa and 398 ±139 MPa respectively. Then at high temperature (1000 °C, under air), the bending strength of Sample A and Sample B reached 337 ±17.1 MPa and 187 ±132 MPa respectively. These results indicated that adequate thick Ni suppressed interfacial reaction between HfB2 composite and interlayer and enabled HfB2 joints reserved the better bending strength even at elevated temperature.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
