RESUMO
A kind of multiscale ß-sialon grain-reinforced Al2O3 matrix composite ceramic tool material, named ASN, was prepared and studied. For the ASN, ß-sialon (molecular formula: Si4Al2O2N6) was synthesized in situ by a hot-pressing and solid-solution reaction process. A total of six samples were prepared at varying sintering temperatures and holding times under vacuum conditions. The solid solution reaction mechanism of ß-sialon, the phase composition, mechanical properties, microstructure, and strengthening and toughening mechanisms of the composite ASN were investigated. As a result, within the experimental parameters, an optimal ASN tool material was obtained under a pressure of 32 MPa and at a temperature of 1550 °C for 20 min. The tested mechanical properties of the optimal sample were as follows: flexural strength 997 ± 59 MPa, fracture toughness 6.4 ± 0.3 MPa·m1/2, Vickers hardness 18.2 ± 0.4 GPa, and relative density 98.1 ± 0.2%. According to crystal defect theory, the solid solution reaction mechanism of in-situ-synthesized ß-sialon in an Al2O3 matrix involves a double mechanism of unequivalence (or hetero-valence) and interstitial filling. The multiscale ß-sialon grains mainly consisted of four grains, which were elongated ß-sialon grains with a diameter of 0.3-0.4 µm and an aspect ratio of 6-9, elongated ß-sialon grains with a diameter of 70 nm and an aspect ratio of 10, ß-sialon whiskers with a diameter of 0.2 µm and an aspect ratio of 12-15, and intragranular ß-sialon whiskers with a diameter of 70 nm. The mechanical properties were improved due to strengthening and toughening mechanisms, such as mixed structure mode (intergranular and transgranular), elongated grain pullout, interface bonding, crack reflection, pinning, and bridging.
RESUMO
OBJECTIVE: To explore clinical significance of rotational axis of distal femur on Chinese adults in total knee arthroplasty (TKA). METHODS: There were 86 Chinese adults (106 normal knees) including 47 males (53 knees) and 39 females (53 knees), 54 knees were on left and 52 on right. The CT scan was employed in the distal femur. The scan direction was aligned to be on the plane perpendicular to the mechanical axis of the femoral. The CT images of cross sections across lateral and medial femoral epicondyle were moved to personal computer,lateral angle between anterior posterior line (APL) and surgical transepicondylar axis (STEA) (ATA),lateral angle between posterior condylar line (PCL) and APL (APA), angle between perpendicularity of APL and PCL (A-PA), posterior condylar angle (PCA), condylar twist angle (CTA), angle between clinical transepicondylar axis (CTEA) and STEA (CSA) were measured. These values were divided into different groups according to gender and side, the values of CTA, PCA, A-PA, angle PT (varus of tibia plateau), constant 3, ATA, APA and constant 90° were compared by statistically. A-PA and PCA, and CTA were analysed statistically with the liner regression, the relationship among CTEA, STEA ,PCL, APL and PLP were performed to assess by liner regression. RESULTS: ATA was (89.79 ± 1.22)°, APA was (84.84 ± 1.83)°, A-PA was (5.16 ± 1.83)°, PCA was (4.80 ± 1.23)°, CTA was (8.23 ± 1.40), CSA was (3.45 ± 0.68)°. All the parameters had no differences on sex and side,but CSA had difference on male and female. There was no difference among angle PT, PCA, A-PA. There was significant difference in CAT, constant 30 and angle PT, PCA,A-PA. There was no difference between ATA and constant 90°, but there was difference between APA and constant 90°. There was relativity between PCA and CTA, and also PCA and A-PA, CTA and A-PA. There was significant relativity between STEA and CTEA, between STEA and APL, between STEA and PCL, and also between APLP, APL and PCL, but there was no significant relativity between PCL and CTEA. CONCLUSION: TKA for Chinese, the section of femoral posterior condyle should be external 5° to obtain the optimum rotational orientation. The property is different entirely between STEA and CTEA, the rotational alignment is not performed according to parallel to the CTEA in distal femur. Among STEA, APL, PCL, the STEA is the most reliable mark ofrotational alignment of the distal femur, and the PCL is the less reliable mark.