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The Mechanical And Deformation Behavior Of Coated Face-centered Cubic High-entropy Alloy

Posted on:2021-02-15Degree:MasterType:Thesis
Country:ChinaCandidate:X T SongFull Text:PDF
GTID:2481306110994489Subject:High-entropy alloys
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A high-entropy alloy(HEA)is defined as an alloy having at least five major metal elements,each having an atomic percentage of5–35%.High-entropy alloy has excellent mechanical properties for novel alloy design,such as high strength,large elongation,exceptional fracture toughness and good corrosion resistance that provide great potential for various industrial applications.However,it is not possess all properties for one class of high-entropy alloy,which restricts its development.For example,the HEA with single-phased Fcc-structured have limited strength but their ductility is low.In general,people use the mechanical treatment and heat-treat to fabricate the Fcc-HEAs with both high strength and high ductility.Coating technology is one of the surface treatment with not change the inner structure and properties.In the paper,The Ni–Mo–P films are successfully coated on the CoCrFeNi high-entropy alloys through electroless plating.The main results are as follow:(1)The yielding strength(?_y)of the coated samples(1 h)shows 260MPa,with a 44.4%improvement,and the ultimate tensile strength)is 760MPa with a?14.4%increment compared with the uncoated samples(?_y=180 MPa,UTS=560 MPa).One is due to the fact that the hard coating can inhibit the propagation of dislocations near the interface.The other is that the repulsive image stress can decrease the driving force of the dislocation emission by counteracting the applied stress.(2)In order to enhance the adherence between the film and substrate,making the coated samples annealing at 400°C for 1h.The surface hardness of the plating for 5 h is around 381HV with dramatically increasing by 121%(H),as compared to the uncoated substrate of172HV.The specimen plating for 1 h,the yield strength(?_y)is 400 MPa with a 62%improvement,and UTS is 732 MPa,increased by 16%in comparison to the substrate(?_y=246 MPa and UTS=630 MPa).The well-matched shear moduli between the film and substrate can make the two phases deform cooperatively in multicomponent HEAs to improve the mechanical properties.(3)A co-existence of the homogeneous flow and shear banding or cracking are studied in the tension of amorphous Ni–Mo–P films on the substrates,which is attributed to the substrate confinement.The deformation mode has a gradual transition from a homogeneous flow to shear banding and cracking via the variation of the film thickness of Ni–Mo–P films,and the deformation mechanism map is acquired.(4)Pile-uped dislocations at the interface of the film and substrate Producing the high-stress concentration,which contributed to the nucleation of cleavage cracks.The crack mode of the coated samples are transforms from the cleavage to quasi-cleavage and eventually to dimples with from the brittle to ductile fracture,as the location away from the interface to substrates gradually.
Keywords/Search Tags:High-entropy alloy, Mechanical behavior, Strength mechanism, Deformation mechanism, Corrosion resistence
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