Effects of Nb and Mo additions on thermal behavior, microstructure and magnetic property of FeCoZrBGe alloy

Both Nb and Mo additions play a vital role in FeCo-based alloys and it is crucial to understand their roles and contents on thermal behavior,microstructural feature and magnetic property of alloys.Nanocrystalline alloy ribbons Fe40Co40Zr9−yMyB10Ge1(y=0–4;M=Nb,Mo)were prepared by crystallizing the as-quenched amorphous alloys.The effects of Nb and Mo additions on structures and properties of the Fe40Co40Zr9B10Ge1 alloy are investigated systemically and compared.With increasing Nb or Mo content,the primary crystallization temperature,grain size ofα-Fe(Co)phase and coercivity Hc all decrease.Moreover,the effect of Mo addition on thermal behavior,microstructure and magnetic properties of the FeCoZrBGe alloy is greater compared to Nb addition.The gap between primary and secondary crystallization peaks of Mo-containing alloys is wider than that of Nb-containing alloys.Both grain size and Hc of Mo-containing alloys are smaller than those of Nb-containing alloys.For Fe40Co40Zr9B10Ge1 alloy,high Mo addition proportion is better compared to high Nb addition proportion.

Impact of Mo/Ni alloying on microstructural modulation and low-temperature toughness of high-strength low-alloy steel

The high-strength low-alloy steel plates with varying Ni/Mo contents were manufactured using the thermos-mechanical control process.The investigation was conducted to explore the effect of Ni/Mo microalloying on microstructure evolution and mechanical properties of the steel.The results revealed that the increase in Ni content from 1 to 2 wt.%reduced the transition temperature of ferrite and the growth range of ferritic grain was narrowed,which promoted grain refinement.The optimized combination of grain size,high-angle grain boundaries(HAGBs),and martensite-austenite(M-A)islands parameter contributed to the excellent impact toughness of S1 steel at-100℃(impact absorbed energy of 218.2 J at-100℃).As the Mo increases from 0 to 2 wt.%,the matrix structure changes from multiphase structure to granular bainite,which increases the average effective grain size to~4.62 pm and reduces HAGBs proportion to~36.22%.With these changes,the low-temperature impact toughness of S3 steel is weakened.In addition,based on the analysis of the characteristics of crack propagation path,it was found that M-A islands with low content(~2.21%)and small size(~1.76 pm)significantly retarded crack propagation,and the fracture model of M-A islands with different morphologies was further proposed.Furthermore,correlation between behaviour of delamination and toughness was further analysed by observing delamination size and impact energy parameters.

Microstructure and creep properties of Ni-based single-crystal superalloys with Mo/Al addition at 760℃/850 MPa

The effect of Mo and Al addition on the microstructure as well as creep rupture properties at760.C/850 MPa was investigated by transmission electron microscopy(TEM)in a Ni-based single-crystal(SC)alloy with the composition of Ni-6.5Al-8.0Mo-2.4Cr-6.2Ta-4.9Co-1.5Re-(0.01-0.05)Y(wt%).The microstructure analysis shows that 0.5 wt%Al addition induces rapid decrease in creep rupture life,and this can be attributed to the formation of dense stacking faults cutting intoγ'precipitates,which can be explained by the increase in Orowan stress caused by the narrowerγchannel width and the decrease in stacking faults energy.Besides,1.5 wt%Mo addition increases the anti-phase boundary energy and decreases the stacking faults energy,resulting in fewer stacking faults and thus a slight decrease in the creep rupture life.

A revisit to the role of Mo in an MP35N superalloy:An experimental and theoretical study

Molybdenum(Mo)has been recognized as an essential alloying element of the MP35N(Co_(35.4)Cr_(22.9)Ni_(35.5)Mo_(6.2),at.%)superalloy for enhancing strength and corrosion resistance.However,a full understanding of the addition of Mo on microstructure and mechanical properties of the Mo-free parent alloy is lacking.In this work,we consider five(Co_(37.7)Cr_(24.4)Ni_(37.9))_(100-x)Mo_(x)(x=0,0.7,2.0,3.2,and 6.2)alloys,and reveal that yield/tensile strength and ductility are continuously increased for these alloys with increasing Mo content while a single-phase face-centered cubic structure remains unchanged.It is found that strong solid solution strengthening(SSS)is a main domain to the improved yield strength,whereas grain boundaries are found to soften by the Mo addition.The first-principles calculations demonstrate that a severe local lattice distortion contributes to the enhanced SSS,and the grain boundary softening effect is mostly associated with the decreased shear modulus.Both first-principles calculations and scanning transmission electron microscopy observations reveal that the stacking fault energy(SFE)reduces by the Mo addition.The calculated SFE value decreases from 0.4 mJ/m^(2) to-11.8 mJ/m^(2) at 0 K as Mo content increases from 0 at.%to 6.2 at.%,and experimentally measured values of SFE at room temperature for both samples are about 18 mJ/m^(2) and 9 mJ/m^(2),respectively.The reduction of SFE promoted the generation of stacking faults and deformation twins,which sustain a high strain hardening rate,thus postponing necking instability and enhancing tensile strength and elongation.

Microstructure and corrosion behavior of Zr–1.0Cr–0.4Fe–xMo alloys

Possibility of using Mo as an alloying element in Zr-based alloys was attractive in terms of microstructure refinement and mechanical properties strengthening. In this research, Zr–1.0Cr–0.4Fe–xMo（0, 0.2, 0.4, and 0.6） alloys with different Mo contents were prepared by vacuum arcmelting method, the microstructure and the corrosion resistance of these alloys were investigated. Addition of Mo has a refinement effect on the microstructure; with the increase of Mo content, the a-laths in the as-cast samples and the grain size in the annealed samples decrease. Zr–1.0Cr–0.4Fe–xMo alloys have large numbers of fine second-phase particles（SPPs） in the matrix, the area fraction of the SPPs is more than 10 %. With the increase of Mo content, the population density of the SPPs increases significantly, while the average diameter of the SPPs decreases. Mo addition also affects the texture; the intensity of basal pole texture aligning normal direction decreases with the increase of Mo content in the alloys.Compared with Zr-4 and Zr–1Nb, Zr–1.0Cr–0.4Fe–xMo alloys have excellent corrosion resistance in 500 ℃/10.3 MPa steam. The corrosion rates of Mo-containing alloys are higher than that of Mo-free alloy, which is mainly attributed to the solute Mo atoms in the Zr matrix.Change of the SPPs features due to the increase of Mo content alleviates the degradation of corrosion resistance in some degree, but it is not the dominant factor.