The Effect Of Boron Addition On The Sintering Mechanism And Properties Of Mo₂FeB₂Based Cermets

In this dissertation, Mo₂FeB₂based cermets were prepared by in-situ reactionsintering process. The Mo₂FeB₂based cermets with different boron additions into rawmaterials were used to probe the change of initial liquid phase sintering temperature.Then Mo₂FeB₂based cermets as clad materials were deposited onto H13substratethrough plasma spraying associated with in-situ reaction sintering process. Themicrostructure and properties of Mo₂FeB₂based cermets and coatings had beensystematically investigated by differential scanning calorimetry （DSC）, X-raydiffraction （XRD）, scanning electron microscopy （SEM）, energy dispersivespectrometer （EDS）, transmission electron microscope （TEM）, and wear and abrasiontest machine.First, the article gave a very detailed overview of the background and researchprogress of ternary boride based cermets. Methods of preparing coatings of Mo₂FeB₂based cermets were summarized. The phase transition of Mo₂FeB₂based cermets wasresearched and summarized in more detail.Secondly, Mo₂FeB₂based cermets of five models were prepared, and theinfluences of boron addition on the sintering mechanism, microstructure andmechanical performance of Mo₂FeB₂based cermets were investigated in theexperiment. It was found that liquid phase sintering temperature of Mo₂FeB₂basedcermets with1.0wt.%～2.0%boron addition reduced. Boron addition contributed toachieve a homogenous and dense sintering microstructure, and then effectivelyimproved the hardness, transverse rupture strength and abrasion resistance of theMo₂FeB₂cermets. The wear mechanism of Mo₂FeB₂based cermets with differentboron additions were studied also. It turned out that the wear mechanism of Mo₂FeB₂based cermets transferred from adhesive wear to fatigue wear.Finally, plasma spraying associated with in-situ reaction sintering process wasselected to make Mo₂FeB₂based cermets coatings onto H13substrates. The hardness,strength, abrasive resistance and porosity of coatings were compared between thecoating without boron addition into power and that with boron addition. It was foundthat adding appropriate amounts of boron into power is good for improving microstructure and performance. The studies also provide new ideas in surfacestrengthening of tool and die steels.