Effect of Ordering on Embrittlement of Ni4Mo Alloy in Hydrogen Gas

The fracture behavior of disordered and ordered Ni4Mo alloy was investigated by tensile tests in hydrogen gas or during hydrogen charging. The results show that the ductility of the disordered alloy decreased slightly with the hydrogen pressure increasing, while that of the ordered alloy decreased rapidly with the hydrogen pressure increasing. However, the ductility of both disordered and ordered alloys reduced similarly seriously with the charging current density increasing. Therefore, the mechanism of order-induced embrittlement of Ni4 Mo alloy in hydrogen gas is supposed to be that atomic order accelerates the kinetics of the catalytic reaction for the dissociation of molecular H2 into atomic H.

Erratum to: New high-strength Ti–Al–V–Mo alloy: from high-throughput composition design to mechanical properties

Erratum to:International Journal of Minerals, Metallurgy and Materials Volume 26, Number 9, September 2019, Page 1151https://doi.org/10.1007/s12613-019-1854-1The original version of this article unfortunately contained a mistake. The presentation of Fig. 11 was incorrect. The correct version is given below:

Densification of Mo Alloys at 1473 K by Adding Ni-Cu Solid Solution

Mo is difficult to sinter densely at a relatively low temperature due to its high melting point. In the present paper,by adding different weight contents of Ni and Cu additives, Mo alloys have been densified at 1473 K for an hour byhot-pressing method, and the optimum contents of Cu and Ni additives have been acquired: when the contents of Niand Cu are 3 and 2 wt pct respectively, the relative density of the sample reaches the maximum value. It was foundthat when the Ni-Cu solid solution was added into Mo alloys. the achieved density is higher than the case of Ni andCu additives. The experimental results indicate that, Ni and Cu play different roles in the process of sintering, theNi-Cu solid solution has the same function as Ni and Cu additives in the course of sintering Mo alloys, It shows moreactivating sintering feature for Mo than the Ni and Cu additives.

Densification of Mo Alloys at 1473K

By choosing different weight contents of Ni and Cu,Mo alloys have been densified under 1473K-30MPa-1h in a vacuum furnace.The experimental results indicate that,when the contents of Ni and Cu are 3wt% and 2wt% respectively,the relative density of the sample reaches the maximum value.Ni and Cu play different roles in the process of sintering,the powder Ni,dissolved in the liquid Cu,shows more activating sintering feature for Mo than the solid Ni.

Texture Evaluation of α_2 Phase in Ti-25Al-10Nb-3V-1Mo Alloy Sheet

The texture evaluation of α2 phase in Ti-25Al-10Nb-3V-1Mo sheet during rolling and annealing has been investigated by means of microstructure observation and ODF analysis. From the weak initial {1010} (1210) and {0001}(1210) textures a {1210}(1010) texture and a {0001}(uvtw)fibre texture are formed after cold rolling. The {0001} (1210) texture is also strengthened simultaneously. The activation process of slip systems is discussed concerning formation of the rolling texture. Because of the disappearance of {0001} (nvtw) fibre texture the primary recrystallization process should occur and the {1210}(1010) texture forms during annealing

Microstructure and tensile properties of Mo alloy synthetically strengthened by nano-Y_2O_3 and nano-CeO_2

Nano-Y2O3 and nano-CeO2 of different weight ratio mixed with deionizing water were doped into MoO2 powder by liquid-solid doping method. The diameter 1.80 and 0.18 mm alloy wires of Mo-0.3Y, Mo-0.3Ce, and Mo-0.15Y-0.15Ce were prepared through reduction, iso- static pressing, sintering, and drawing. Tensile properties, second phase microstructure and fracture surface appear- ance of wires were analyzed. The better refining effect for Mo alloy powder can be gotten after two kinds of nano- particle oxide doped into MoO2 than only one doped. Nano-Y2O3 and nano-CeO2 have different influences on sintering process. For nano-CeO2, the constraining effect of grain growth focuses on the initial sintering stage, nano- Y2O3 plays refining grains roles in the later densification stage. Nano-Y2O3 is undistorted and keeps intact in the process of drawing; and nano-CeO2 is elongated and bro- ken into parts in the drawing direction. The strengthening effect of nano-Y2O3 and nano-CeO2 keeps the finer grains and superior tensile properties for Mo-0.15Y-0.15Ce wire.

Preparation and bioactive surface modification of the microwave sintered porous Ti-15Mo alloys for biomedical application

Biomedical porous Ti-15 Mo alloys were prepared by microwave sintering using ammonium hydrogen carbonate（NH4HCO3） as the space holder agent to adjust the porosity and mechanical properties. The porous Ti-15 Mo alloys are dominated by β-Ti phase with a little α-Ti phase, and the proportion of α and β phase has no significant difference as the NH4HCO3 content increases. The porosities and the average pore sizes of the porous Ti-15 Mo alloys increase with increase of the contents of NH4HCO3, while all of the compressive strength, elastic modulus and bending strength decrease. However, the compressive strength, bending strength and the elastic modulus are higher or close to those of natural bone. The surface of the porous Ti-15 Mo alloy was further modified by hydrothermal treatment, after which Na2Ti6O13 layers with needle and flake-like clusters were formed on the outer and inner surface of the porous Ti-15 Mo alloy. The hydrothermally treated porous Ti-15 Mo alloy is completely covered by the Ca-deficient apatite layers after immersed in SBF solution for 14 d, indicating that it possesses high apatiteforming ability and bioactivity. These results demonstrate that the hydrothermally treated microwave sintered porous Ti-15 Mo alloys could be a promising candidate as the bone implant.

Enhancing the high-temperature creep properties of Mo alloys via nanosized La_(2)O_(3) particle addition

Molybdenum(Mo) alloys with different La_(2)O_(3)particle additions(0.6,0.9,1.5 wt.%) were prepared by powder metallurgy to investigate the effect of La_(2)O_(3)particles on microstructural evolution and creep behavior of the alloy.Pure Mo,annealed at 1500℃ for 1 h,presented a fully recrystallized microstructure characterized by equiaxed grains.The alloys doped with La_(2)O_(3)particles(Mo-La_(2)O_(3)alloys),on the other hand,exhibited fibrous grains elongated in the rolling direction of the plate.In contrast to the shape of the grains,the average grain size of the alloys was found to be insensitive to the addition of La_(2)O_(3)particles.Nanosized La_(2)O_(3)particles with diameters ranging from 65 to 75 nm were distributed within the grain interior.Tensile creep tests showed that dislocation creep was the predominant deformation mode at intermediate creep rate(10^(-7)s^(-1)-10^(-4)s^(-1)) in the present alloys.The creep stress exponent and activation energy were found to decrease with increasing temperature,particularly within the low creep rate regime(<10^(-7)s^(-1)).The Mo-La_(2)O_(3)alloys exhibited remarkably greater apparent stress exponent and activation energy than pure Mo.A creep constitutive model based on the interaction between particles and dislocations was utilized to rationalize the nanoparticle-improved creep behavior.It was demonstrated that low relaxed efficiency of dislocation line energy,which is responsible for an enhanced climb resistance of dislocations,is the major creep strengthening mechanism in the Mo-La_(2)O_(3)alloys.In addition,the area reduction and creep fracture mode of the Mo-La_(2)O_(3)alloys were found to be a function of the creep rate and temperature,which can be explained by the effect of the two parameters on the creep and fracture mechanisms.

Local deformation and processing maps of Ti-24Al-17Nb-0.5Mo alloy

The processing maps were used to identify the optimal forging parameters of Ti-24A1- 17Nb-0.5Mo alloy by evaluating the flow data according to the DMM model. The actual local strain rate and strain distribution in the samples were obtained by finite element calculations. The local microstructures of the deformed samples were related to the local deformation parameters and correlated with the processing maps at 0.3, 0.4, 0.5 and 0.6 of logarithmic strain. Flow regimes predicted by DMM analysis were then correlated with the local microstructural observations. Five domains of efficient coefficient could be distinguished. Unstable regions were microstructurally related to shear band formation within the （~2~B2 phase deformation field, and to flow localiza- tion at grain boundaries of B2 phase in the near B2 phase deformation field. Stable flow regimes were shown to be associated with dynamic globularization of the plate- like a2 in the a2＋B2 phase deformation zone, and with dynamic recrystallization of B2 in the near B2 phase deformation zone.

Effects of solution treatment and cold rolling on structure and tensile properties of hot-rolled Ti-7.5Mo alloy

The effects of solution treatment(ST)and cold rolling(CR)on structure and tensile properties of a heavily hot-rolled(HR)Ti–7.5Mo alloy were investigated.Experimental results indicated that,after HR with a one-pass 65%reduction in thickness,the pores in as-received samples substantially disappeared,the misorientation angle distribution became broader,and grain texture shifted toward<10-10>.Post-HR ST produced an orthorhombicα''-phase with fine needle-type morphology and caused misorientation to narrow down to 55°–65°with substantially random texture;post-ST CR caused misorientation shift toward high-angle side and texture toward<10-10>and<2-1-10>.With an increase in reduction in thickness,α'(102)intensity increased at the expense of two adjacent(112)/(022)α''-peaks.All X-ray diffraction,metallography and electron backscattered diffraction on scanning electron microscope results indicated that pre-ST HR did not affect the formation of the desired low-modulusα''-phase when the alloy was subsequently solution-treated.From a practical point of view,the most optimal tensile properties may be found in the sample solution-treated at 900°C for 30 min and cold-rolled by a 20%reduction in thickness,which demonstrated a yield strength of 924 MPa,an ultimate tensile strength of 933 MPa,a tensile modulus of 73 GPa,and an elongation of 26%.

Brazeability evaluation of Ti-Zr-Cu-Ni-Co-Mo filler for vacuum brazing TiAl-based alloy

Ti-47Al-2Nb-2Cr-0.15B(mole fraction,%)alloy was vacuum brazed with amorphous and crystalline Ti.25Zr-12.5Cu-12.5Ni-3.0Co-2.0Mo(mass fraction,%)filler alloys,and the melting,spreading and gap filling behaviors of the amorphous and crystalline filler alloys as well as the joints brazed with them were investigated in details.Results showed that the amorphous filler alloy possessed narrower melting temperature interval,lower liquidus temperature and melting active energy compared with the crystalline filler alloy,and it also exhibited better brazeability on the surface of the Ti.47Al.2Nb.2Cr.0.15B alloy.The TiAl joints brazed with crystalline and amorphous filler alloys were composed of two interfacial reaction layers and a central brazed layer.Under the same conditions,the tensile strength of the joint brazed with the amorphous filler alloy was always higher than that with the crystalline filler alloy.The maxmium tensile strength of the joint brazed at 1273 K with the amorphous filler alloy reached 254 MPa.

Microstructure evolution and mechanical properties of laser additive manufactured Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy

The microstructure, microhardness and tensile properties of laser additive manufactured (LAM) Ti?5Al?2Sn?2Zr?4Mo?4Cr alloy were investigated. The result shows that the microstructure evolution is strongly affected by the thermal history of LAM process. Primary α (αp) with different morphologies, secondary α (αs) and martensite α' can be observed at different positions of the LAMed specimen. Annealing treatment can promote the precipitation of rib-like α phase or acicular α phase. As a result, it can increase or decrease the microhardness. The as-deposited L-direction and T-direction specimens contain the same phase constituent with different morphologies. The tensile properties of the as-deposited LAMed specimens are characterized of anisotropy. The L-direction specimen shows the character of low strength but high ductility when compared with the T-direction specimen. After annealing treatment, the strength of L-direction specimen increases significantly while the ductility reduces. The strength of the annealed T-direction specimen changes little, however, the ductility reduces nearly by 50%.

Microstructure and compression properties of fine Al2O3 particles dispersion strengthened molybdenum alloy

The Mo alloys reinforced by Al2O3 particles were fabricated by hydrothermal synthesis and powder metallurgy. The microstructures of Mo-Al2O3 alloys were studied by using XRD, SEM and TEM. The results show that Al2O3 particles, existing as a stable hexagonal phase(α-Al2O3), are uniformly dispersed in Mo matrix. The ultrafine α-Al2O3 particles remarkably refine grain size and increase dislocation density of Mo alloys. Moreover, a good interfacial bonding zone between α-Al2O3 and Mo grain is obtained. The crystallographic orientations of the interface of the Al2O3 particles and Mo matrix are [111]a-Al2O3//[111]Mo and(112)a-Al2O3//(0 11)Mo. Due to the effect of secondary phase and dislocation strengthening, the yield strength of Mo-2.0 vol.%Al2O3 alloy annealed at 1200 ℃ is approximately 56.0% higher than that of pure Mo. The results confirm that the addition of Al2O3 particles is a promising method to improve the mechanical properties of Mo alloys.

Shear localization behavior in hat-shaped specimen of near-αTi−6Al−2Zr−1Mo−1V titanium alloy loaded at high strain rate

The microstructure characteristics in early stage shear localization of near-αTi−6Al−2Zr−1Mo−1V titanium alloy were investigated by split Hopkinson pressure bar(SHPB)tests using hat-shaped specimens.The microstructural evolution and deformation mechanisms of hat-shaped specimens were revealed by electron backscattered diffraction(EBSD)method.It is found that the nucleation and expansion of adiabatic shear band(ASB)are affected by both geometric and structural factors.The increase of dislocation density,structure fragment and temperature rise in the deformation-affected regions provide basic microstructural conditions.In addition to the dislocation slips,the extension twins detected in shear region also play a critical role in microstructural fragmentation due to twin-boundaries effect.Interestingly,the sandwich structure imposes a crucial influence on ASB,which finally becomes a mature wide ASB in the dynamic deformation.However,due to much larger width,the sandwich structure in the middle of shear region is also possible to serve as favorable nucleation sites for crack initiation.

Mechanical Properties of DS NiAl/Cr(Mo) Alloys with Low Addition of Hf for High-temperature Applications

A multiphase NiAl-28Cr-5.85Mo-0.15Hf alloy, which was directionally solidified （DS） in an Al2O3-SiO2 mold by standard Bridgman method and then underwent prolonged solution and aging treatment was prepared. The microstructure, tensile properties as well as tensile creep of the heat-treated alloy at different temperatures were studied. The alloy was composed of NiAI, Cr（Mo） and Hf-rich phase and small amount of fine Heusler phase （Ni2AlHf）. Although the present alloy exhibited high tensile strength at low temperature, it was weaker than that of system with high content Hf but still stronger than that of many NiAl-based alloys at high temperatures. The fracture toughness is lower than that of DS NiAl-28Cr-6Mo alloy. Nevertheless, advantageous effects on the mechanical properties, i.e. the decrease in brittle-to-ductile transition temperature （BDTT） were obtained for the low content of Hf. The obtained creep curves exhibit conventional shape： a short primary creep and long accelerated creep stages. The rupture properties of the heat-treated alloy follow the Monkman-Grant relationship, which exhibits similar creep behavior to that of NiAl/Cr（Mo） system with high Hf content.

Mechanical behaviors of NiAl-Cr(Mo)-based near eutectic alloy with Ti, Hf, Nb and W additions

Effects of Ti, Hf, Nb and W alloying elements addition on the microstructure and the mechanical behaviors of NiAl-Cr（Mo） intermetallic alloy were investigated by means of XRD, SEM, EDX and compression tests. The results show that Ni-31Al-30Cr-4Mo-2（Ti, Hf, Nb, W） alloy consists of four phases： NiAl, ？？Cr solid solution, Cr2Nb and Ni2Al（Ti, Hf）. The mechanical properties are improved significantly compared with the base alloy. The compression yield strength at 1 373 K is 467 MPa and the room temperature compression ductility is 17.87% under the strain rate of 5.56？？0-3 s-1, due to the existence of Cr2Nb and Ni2Al（Ti, Hf） phases for strengthening and Ti solid solution in NiAl matrix and coarse Cr（Mo, W） solid solution phase at cellular boundaries for ductility. The elevated temperature compression deformation behavior of the alloy can be properly described by power-law equation： ε=0.898 σ8.47exp[-615/（RT）].

TEMPERATURE DEPENDENCE OF PERMEABILITY OF Co_(66)Fe_4Mo_2Si_(16)B_(12) ALLOY

At different annealing temperatures, the saturation magnetostrictions and the correlation between the permeability μi and the temperature T （μi-T curves） of the Co66Fe4Mo2Si16B12 alloy were investigated using a small-angle magnetization tester and core tester. The experimental results showed that the μi-T curves had different shapes at different ranges of annealing temperature; the permeability μi of the alloy improved with the increase of the annealing temperatures below 460℃; when the alloy was annealed above 480℃, the poor magnetic properties were considered to be caused by larger saturation magnetostriction.

Effect ofαphase morphology on fatigue crack growth behavior of Ti−5Al−5Mo−5V−1Cr−1Fe alloy

Taking a Ti−5Al−5Mo−5V−1Cr−1Fe alloy as exemplary case,the fatigue crack growth sensitivity and fracture features with various tailoredαphase morphologies were thoroughly investigated using fatigue crack growth rate(FCGR)test,optical microscopy(OM)and scanning electron microscopy(SEM).The tailored microstructures by heat treatments include the fine and coarse secondaryαphase,as well as the widmanstatten and basket weave features.The sample with coarse secondaryαphase exhibits better comprehensive properties of good crack propagation resistance(with long Paris regime ranging from 15 to 60 MPa·m1/2),high yield strength(1113 MPa)and ultimate strength(1150 MPa),and good elongation(11.6%).The good crack propagation resistance can be attributed to crack deflection,long secondary crack,and tortuous crack path induced by coarse secondaryαphase.

Superplasticity of a Ti-24Al-14Nb-3V-0.5Mo Intermetallic Alloy

Superplastic properties and microstructural evolution of a Ti-24Al-14Nb-3V-0.5Mo (at. pct) intermetallic alloy were studied. Optimum superplastic properties were obtained for temperatures in the interval 960℃≤5 T≤5980℃. The apparent activation energy in the superplastic regime was determined and the deformation mechanism was also discussed. Based on the studies, a curve panel with three sheets sandwich structure was fabricated successfully. The microstructures corresponding to different strain in the part were also studied.

Formation and Oxidation Resistance of Silicide Coatings for Mo and Mo-Based Alloys

The forming process of silicide coatings on pure Mo and Mo-base alloys, obtained by the gas- phase deposition method. has been studied by examining the microstructure of coatings and the relationship between coating thickness and process parameters. It was shown that the growth of coatings was diffusion-controlled, the diffusion of silicon to be coated into Mo or Mo-base alloys was mainly responsible for the formation of silicide. The relationship between initial silicide thickness and oxidation resistance was also investigated, and the equation of service life of the coatings at high temperature in air is presented.