| Recently, researchers discovered a ternary compound AlMgB14, which hasbeen given great attentions for its excellent properties such as super-hardness,good wear-resistance, and high chemical stability etc. It is a new member in thesuper-hard material after diamond, c-BN and BXC. It was reported that theVickers hardness of AlMgB14are27.4-28.3GPa,32-35GPa for singal crystaland polycrystal, respectively. The highest microhardness ofAlMgB14-TiB2ceramic matrix composite could reach46GPa after addingultra-fine grained TiB2which evenly distributed in the AlMgB14matrix. The costof scale production of AlMgB14and AlMgB14-TiB2composite is far less thandiamond and c-BN. Thus, AlMgB14and AlMgB14-TiB2composite have a brightfuture for application in the field of cutting tools, abrasives, wear resistantcoatings, key components in aerospace and military and so on.AlMgB14and AlMgB14-TiB2composites with different ultra-fined grainedTiB2content were synthesized at1400°C under a pressure of60MPa by usingadvanced FAPAS (Field Activated Pressure Assisted Synthesis) process. Themicrohardness and fracture toughness of samples were characterized by using indentation method. The strengthening mechanism of ultra-fined grained TiB2toAlMgB14matrix was primarily investigated through observing the identationcracks by using a micro-hardness tester and scanning electron microscope.The friction and wear behavior of AlMgB14-30wt.%TiB2composite wascharacterized at the temperature range of25°C-800°C by a HT-1000typereciprocating ball-on-disk high temperature tribometer. The morphologies andelement distribution of the scar of friction couple were analyzed by using XRD,SEM and EDS methods.By using Thermal Gravity analyzing method, the oxidation resistance ofAlMgB14-30wt.%TiB2composite at the temperature range of600°C-1000°C for10h was investigated.The phase changes of the oxidation layer were examinedby using XRD. The microstructure of both the oxidation surface and thecross-section of the oxidized specimens were characterized by using SEM、EDS and other analyzing methods. Meanwhile, the forming process of oxidelayer is also primarily discussed.The results show that the hardness and fracture toughness of AlMgB14improve noticeably after adding ultra-fined grained TiB2to AlMgB14matrix.Theaverage microhardness of AlMgB14-30wt.%TiB2composite is32.5GPa, themaximum value of fracture toughness coule reach4.15MPa·m1/2.Frictioncoefficient of AlMgB14-30wt.%TiB2composite is in the range of0.12and0.65in the temperature range of25°C-800°C at a load of10N and sliding speed of Wear mechanism varies from Mild abrasive scratches at low temperature toadhesive wear at higher test temperatures. At800°C, the friction coefficient ofAlMgB14-30wt.%TiB2composite is0.12as lubiricious oxidation products withthe presence of TiO2formed on the worn surface,this composite present anexcellent self-lubrication and anti-wear properties. The oxidation kinetics ofAlMgB14-30wt.%TiB2composite is in agreement with the parabolic law with anactivation energy of176±20KJ·mol-1from700°C to1000°C.The thickness ofthe oxidized layer significantly changes from about4.1μm at700°C to about84μm at1000°C. Only TiB2phase is oxidized at the oxidation temperature of700°C and the mass change is very small. AlMgB14is being oxidized at800°C,andMgO(B2O3)2and (Al2O3)10(B2O3)2phases form in the oxide layer. Whenoxidized at1000°C for10h,the mass change rate is about6.75℅. Meanwhile, theoxide layer is divided in three parts: the outer glassy B2O3layer, the middlelayer contained mixed oxides and small pores, and the underlying reaction layercontained large pores and TiB2phase which has not been oxidized. |
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