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The Research Of NiAl Coatings Prepared By SHS Reaction On Q235

Posted on:2014-07-30Degree:MasterType:Thesis
Country:ChinaCandidate:L K ZhaoFull Text:PDF
GTID:2251330422451017Subject:Materials Processing Engineering
Abstract/Summary:PDF Full Text Request
NiAl intermetallic compound has a high melting point, high hardness, lightweight, high thermal conductivity, oxidation resistance, high temperature stabilityand other excellent performance. In the coatings material, it has good applicationprospects. In this paper, with SHS coating preparation and joining technology, NiAlintermetallic compound coatings are prepared on Q235, Which includes two ways:SHS direct joining and SHS indirect joining (add intermediate joining layer). BySEM, EDS, XRD and mechanical properties testing, microstructure and mechanicalproperties of joining interface of NiAl coatings and substrate are analyzed. And theinterface formation mechanism is described. NiAl coatings surface microstructurewas analyzed and tribological properties of the coatings to be explored, to obtain ahigh binding capacity, high reliability NiAl coatings.When NiAl coatings are prepared by SHS direct joining technology, NiAlcoating and the substrate achieve a successful joining rely on the exothermic ofreaction system. Reaction system which Ni, Al atomic ratio is1:1is ignited by TIGarc. When self-propagating reaction ignited at room temperature, the combustionwave goes out in the middle. Preheating the NiAl coatings and substrate, thecombustion wave spread smoothly and to achieve the joining of NiAl coating andthe substrate. In the SHS process, NiAl exothermic reaction causes the melting of Alof system. Part of Al enrichs in the surface of the substrate and Fe of the substrate isdissolved to liquid Al. In joining interface, Mutual dissolution and diffusion occursand Fe-Al intermetallic compound is generated. Interfacial organizations were: NiAl/Ni2Al3+Ni+Ni3Al/FeAl2/FeAl/Fe3Al/substrate. Shear strength of joining interfaceincreases with the increase of the joining pressure, and with the increase ofpreheating temperature shear strength also show an increasing trend. Shear strengthof joining interface up to16.26MPa. Reaction mechanism of joining interface iselaborated when NiAl coatings prepared by SHS direct joining. Generating liquid Alof NiAl reaction system in the combustion process is the key to join.When NiAl coating are prepared by SHS indirect joining technology, NiAlexothermic reaction results in the melting of Cu-Zn solder, and the molten solderwets the substrate to achieve a better joining. When self-propagating reaction isperforming, the molten solder and the NiAl reaction system near the substrate fusewith each other and the diffusion reaction occurs in the joining interface. Finally,miscible region forms here, and miscible region close to the substrate and form abetter connection. Shear strength of joining interface increases with the increase of the joining pressure, but with the increase of preheating temperature shear strengthshow a decreasing trend. Shear strength of joining interface up to60.83MPa.Reaction mechanism of joining interface is elaborated when NiAl coatings preparedby SHS indirect joining.With the increase of joining pressure and the preheating temperature, NiAlcoating density is increased. And in the case of preheating, NiAl coating surface isall of NiAl intermetallic compound wanted. Derived from the friction and wear test,NiAl coatings prepared have low friction coefficient and good wear resistance.Finally the reaction mechanism of the synthesis of NiAl intermetallic compound iselaborated.
Keywords/Search Tags:NiAl coatings, SHS joining, intermediate joining layer, joining interface
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