Strategy of preparing SmCo based films with high coercivity and remanence ratio achieved by temperature and chemical optimization

SmCo based films with excellent intrinsic magnetic properties have promising applications in micro-electro-mechanical system(MEMS).However,due to the complexity of phase composition and uncontrollable crystallization degree of SmCo hard magnetic phase in the film,both the coercivity(Hc)and remanence(Mr)of films are difficult to enhance simultaneously.In this paper,SmCo based films were deposited with a Cr underlayer and capping layer on single crystal Si substrates via magnetron sputtering process.The effects of annealing parameters and Sm/Co atomic ratio on the phase structure and coercivity of films are discussed.By adjusting the Sm/Co atomic ratio from 1:5 to 1:4,Co soft magnetic phase disappears and the single phase SmCo5 is obtained,leading to the increase of coercivity of the films from 30 to 34 kOe.The influence of deposition temperature and Cu doping on magnetic properties of SmCo based films was investigated.When the deposition temperature increases from room temperature to 250℃,the coercivity will further increase from 34 to 51 kOe.However,a severe kink is observed in the demagnetization curves due to the poor exchanged coupling.An analysis of transmission electron microscopy(TEM)confirms that the average size of non-hard magnetic amorphous phase exceeds the effective exchanged coupling length of SmCo5,which contributes to the decoupling and low remanence ratio.Therefore,doping Cu and applying a post-annealing process can significantly improve the crystallization degree of the films.Both the coercivity and the remanence ratio of the demagnetization curves are greatly enhanced.We propose a plausible strategy to prepare the SmCo based films with high coercivity and remanence ratio by temperature and chemical optimization,which can be utilized in high performed MEMS devices.

Microstructure Evolution,Tribological and Corrosion Properties of Amorphous Alloy Strengthening Stainless Steel Fabricated by Selective Laser Melting in NaCl Solution

As a type of austenitic stainless steel,316L stainless steel has excellent plasticity,corrosion resistance,and biocompatibility,making it widely used in industries,especially in the marine environments.However,its lower yield strength and wear resistance are the obvious disadvantages that restrict its application in more fields.In this work,an Fe-based amorphous alloy(Fe^(am))was selected as reinforcement to enhance the 316L stainless steel prepared by selective laser melting(SLM),and microstructure evolution,mechanical properties,tribological and corrosion performance of the SLMed samples were investigated in detail.The relative density values of both 316L stainless steel and Fe^(am)-reinforced samples are above 99%,which suggests that Fe^(am)-reinforced samples also have outstanding formability.In the as-etched micrograph,all of the SLMed samples exhibit cellular structure.Fe^(am)-reinforced samples have thicker sub-grain boundaries,and retained amorphous phase can be observed in the samples reinforced with 10 wt%and 15 wt%Fe^(am).As the addition of Fe^(am) increases,the microhardness and compression strength of the Fe^(am)-reinforced samples gradually improve and reach 449.2 HV and 2181.9 MPa,respectively.The wear morphologies show that the 316L stainless steel and Fe^(am)-reinforced samples both experience abrasive wear and corrosion wear in a 3.5 wt%NaCl solution.Meanwhile,as the amount of Fe^(am) added increases,the coefficient of friction and wear rate of SLMed samples gradually decrease.Compared to the unreinforced sample,Fe^(am)-reinforced samples have lower corrosion current density and higher pitting potential according to the potentiodynamic polarization curves and also exhibit superior corrosion resistance in the salt spray environment.This work suggests that the addition of Fe-based amorphous alloy can improve the mechanical properties and wear resistance of 316L stainless steel,as well as its ability to withstand salt spray corrosion.

Nucleation barrier height in undercooled metallic melts

The phase-field model of a liquid-to-solid transition was constructed where the model parameters were linked quantitatively to the interfacial properties, and the variation of nucleation barrier height in undercooled metallic melts with respect to undercooling was studied respectively based on two kinds of forms of local free energy density. The calculation results show that, with the increase of undercooling, the critical nucleus does not show bulk properties, and the nucleation barrier height decreases gradually and deviates more and more from that predicted by the classical nucleation theory in both cases. The physical spinodal occurs for a specific form of the local free energy density, where the nucleation barrier height vanishes when the undercooling reaches a critical value and the reduced nucleation barrier height can be expressed by a function of the ratio of undercooling to critical undercooling.