WU An-hua, CAO Wen-bin, LI Jiang-tao, GE Chang-chun. Solid State Sintered SiC Ceramics[J]. Journal of Materials Engineering, 2001, 0(4): 3-5.
Solid state sintered SiC ceramics were obtained by hot pressing of α-SiC, β-SiC and 1%α-SiC+99%β-SiC powders with boride and carbon as additives.Two phase transforms of 3C→6H and 6H→4H occurred during sintering process.The in situ toughening SiC ceramics can’t be obtained only by rod-like grains without the weak grain-boundary.
LI Guo-qiang, LI Di, LI Jiu-qing, GUO Bao-lan, PENG Ming-xia. A New Type of Ce-Mo Based Conversion Coatings for Al-alloys[J]. Journal of Materials Engineering, 2001, 0(4): 6-9.
A new type of process for forming Ce-Mo based conversion coatings on Al-alloys was developed.Conversion coatings about 3-6μm thickness were obtained by immersing Al-alloys in boiling film formation solution containing (NH4)2Ce(NO3)6 2.5g/L, NaKC4H4O6·4H2O2.5g/L, Na2CO3 7.5g/L and Na2MoO45.0g/L for 20 minutes.In the case of LF6 alloy, polarization curves and immersion tests in 5% NaCl indicated that the conversion coatings exhibited more excellent resistance to localized corrosion than the conventional chromate conversion coatings.However, its resistance to localized corrosion was not satisfactory on LC4 Al alloy.Energy dispersion analyzer of X-ray (EDAX) analysis revealed that the conversion coatings formed on LF6 and LC4 Al-alloys consists mainly of oxides and hydroxides of Al, Ce and Mo.However, their surface microstructure was quite different, which might be contribution to explain their difference in corrosion inhibition.
YUAN Guang-yin, ZENG Xiao-qin, LÜ Yi-zhen, DING Wen-jiang, SUN Yang-shan. Mechanical Properties Improvement of Mg-Al Based-Alloy with Sb Addition[J]. Journal of Materials Engineering, 2001, 0(4): 10-15.
Small amount (0.4wt%-0.7wt%) of Sb addition to the Mg-Al based alloy AZ91(Mg-9Al0-8Zn) resulted in significant increase in the yield strength at both ambient and elevated temperatures up to 200℃, By using SEM and TEM the change of microstructure of specimens before and after deformation was investigated in detail and the results indicated that the microstructure was fined effectively by the Sb addition.Sb in AZ91 exists-in two forms:(1)precipitated in form of Mg3Sb2 particle with hexagonal structure(D52 type); (2) soluted in β-Mg17Al12.phase.Metallographic observation and theory calculation showed that the primary α-Mg could nucleated on Mg3Sb2 particle surface.The reason of improved mechanical properties by Sb was discussed:The RT strengthening mechanism of alloys containing Sb was fine grain strengthening resulted from dispersoids(Mg3Sb2) fining the matrix-grain and the improvement of mechanical properties at elevated temperatures mainly resulted from the dispersion strengthening of Mg3Sb2 dispersoids.
CAI Shu, YUAN Qi-ming, MENG Jia-hong, CHEN Yu-ru, YANG Zheng-fang. Study on the Low-temperature Ageing of ZTM15 (2Y)/Al2O3 Composites[J]. Journal of Materials Engineering, 2001, 0(4): 16-18.
A microstructure with a narrow ZrO2 grain size distribution in the fine mullite grain matrix was obtained by the addition of 5vol%～10vol%Al2O3 particles. The effect of Al2O3 particles on the low tempe-rature ageing of ZTM15(2Y)/Al2O3 composites was studied. The result shows that compared with ZTM15(2Y), the room temperature mechanical properties of ZTM15(2Y)/Al2O3 composites, especially the toughness, are remarkably improved, and toughness could reach 7.8MPa·m1/2.The microcraking is the dominant toughening mechanism.The addition of Al2O3 particles could not inhibit the degradation behavior of ZTM15(2Y) because of the increase of microcraks, on the contrary, enhanced t-m transformation during ageing.
TAO Xiao-la, HU Yong-ming, YI Xiao-su. Indenter Depth-Contact Force-Resistance Relation of Polymer Based-Carbon Fiber Laminates under Quasi-static Indentation Conditions[J]. Journal of Materials Engineering, 2001, 0(4): 19-21.
In accordance with ASTM D6264-98 test method, the indenter depth-contact force-resistance relation and the resistance time relation of epoxy based carbon fiber laminates were simultaneously measured with respect to the variation of electrodes.The investigation explored and expanded the ASTM standard, made a simultaneous detect of concentrated indentation-induced damage of composite laminates possible.
YANG Zu-pei, QU Shao-bo, CUI Bin, GAO Feng, HOU Yu-deng, TIAN Chang-sheng. The Fabrication and Dielectric-temperature Stability of Different Based Composite Ceramics[J]. Journal of Materials Engineering, 2001, 0(4): 22-24.
By the method of mixed sintering, the composite ceramics consisting of two phases with PZN-based and PMN-based respectively were successfully prepared.The experiments show that the composite ceramics exhibit high dielectric constant(5377) with flat temperature characteristic over a wide ranges of 15℃ to+90℃,which could be attributed to the separation of the low temperature phase (paraelectric phase) from the high temperature phase (polar microregions) in composite ceramics.
ZHAO Peng-fei, KANG Hui. Study on Vacuum Brazing of Dissimilar Alloys of Al-Ti[J]. Journal of Materials Engineering, 2001, 0(4): 25-28.
The existence of brittle,stratiform and hard intermetallic compound(TiAl3,TiAl and Ti3Al) in the conjunction interface is the primary problem for the welding of dissimilar alloys of Al and Ti.Based on newest development and documents published in relevant fields, by using the principals of orthogonal experiment, based on the alloy of-Al-11.5Si,9 types of brazing filler metals were confected by adding alloying elements Sn and Ga to Al-11.5Si close-eutectic alloys.The overall properties of the brazing filler metals were judged by anti-shear-test,wettability experiments We tried to make a new proper brazing filler metal to braze the dissimilar alloys of Al and Ti alloys from it.The testing results showed that the brazing filler metal of Al-11.5Si close-eutectic alloys containing 10%Sn, 0-20%Ga has better property on extendibility and anti-shear intensity, and the component of dissimilar alloys of aluminum and titanium has better mechanical property than others when the brazing filler metal used to braze.
ZHANG Yun, DENG Hai-jin, LI Ming, LI Dong-sheng, JIANG Hai. The Evaluation of Graphitization Degree P1 Model and Measurement of C/C Composites[J]. Journal of Materials Engineering, 2001, 0(4): 29-33.
The graphitization degree is one of the most important structural parameters of C/C composites.But it is difficult to be exactly measured for their multiformity.The probability for adjacent hexagonal layer planes in parallel to regular graphitic stacking (P1) is the most exact evaluation of the development of graphitic structure in carbon materials.The P1 of series of C/C composites in different heat-treated temperture (HTT) are obtained from computer computation according to the shape but not the position of of XRD peaks.The results show that P1 can characterize the graphitization degree of C/C composites satisfactorily-In addition, the relation between the garphitization degree of C/C composites and HTT was discussed in this paper.
TANG Jian-xin, MI Qing-tian, ZHANG Ai-bin, CHEN Jian-pin. Method of Adhesion Strength and Spray Techniques of Detonation Gun Sprayed WC-Co Coatings[J]. Journal of Materials Engineering, 2001, 0(4): 34-36.
A new method has been introduced to measure the adhesion strength of the d-gun sprayed WC-Co coatings.The pulling critical size has been analyzed.The experiments show that the pulling critical size is about 2mm for detonation-spraying gun made in China and the adhesion strength for WC-Co coating is as high as 143MPa.It has indicated that the value of O2/C2H2 mol ratio must be 1.5 in order to avoid the oxidation of Co during spraying and obtain good microstructure.
ZHU Shi-zhen, WANG Shu-jun. A Study on Microstructure and Properties of SiCf/SiC Composite Fabricated by FCVI[J]. Journal of Materials Engineering, 2001, 0(4): 37-39.
SiCf/SiC composite was fabricated by forced flow thermal-gradient chemical vapor infiltration (FCVI).The density of composite is 2.3g/cm-3.The flexural strength and fracture toughness of SiCf/SiC compsites were tested:the flexural strength is 291 MPa, the fracture toughness is 11.4 MPa·m1/2.The microscopy structure was characterized by SEM, TEM and X-ray diffraction.The results show that SiC matrix fabricated by FCVI is β-SiC, which has sub-micron grain size and good crystallinity-And the toughening mechanism was also investigated by morphology of the fractrue surface.
DING Chuan-fu, LIU Jian-zhong, HU Ben-run, WU Xue-ren, LI Shu-bai. Explanation of the Standard Test Method for Measurement of Small Fatigue Crack Growth Rate of Metallic Materials[J]. Journal of Materials Engineering, 2001, 0(4): 40-43,47.
Compiling background of an aero-standard test method for measurement of small fatigue crack growth rates was outlined-Several main technical problems for the method were demonstrated,such as choice of specimens and methods of monitoring small-crack, determi-nation of three-dimensional (3D) stress intensity factor,small-crack non-interacting criteria as well as physical small-crack threshold-Comparision was also made between this method and Appendix X3 on ASTM test method E647-95a.
JIANG Chuan-hai, WANG De-zun, WU Jian-sheng. Determination for the Yield Strength of Matrix in a SiCw/Al Composite by the X-ray Diffraction[J]. Journal of Materials Engineering, 2001, 0(4): 44-47.
According to the principle of-stress measurement by X-ray diffraction, the test method of matrix yield strength in composites was established.The actual yield strength of matrix in a 20vol%SiCw/Al composite was measured.The results show that, the matrix yield strength in the composite is obviously higher than that of single matrix material.The matrix strengthening in the composite is mainly due to high dislocation density and fine sub-gain.
