Role of chromium on mechanical properties of Fe-Mn-Ni-Mo-Ti maraging steels

This experiment investigated the role of chromium in the mechanical properties of Fe-5Mn-9Ni-5Mo-1.5Ti maraging steels containing up to 3% chromium. Remarkable age-hardening responses were observed in the Fe-5Mn-9Ni-5Mo-1.5Ti and Cr-bcaring alloys. A ductile-brittle-ductile transition occurred in the Cr-bearing alloys during isothermal aging below 510°C. This was due to the segregation of titanium and manganese to prior austenite grain boundaries and their subsequent desegregation into the matrix. The addition of chromium to the base alloy considerably improved its ductility after aging at 520°C. From microstructure and AES analyses, it is suggested that chromium addition augments the volume fractions of (Fe,Mn)₂Mo and η-Ni₃Ti precipitates in the Fe-5Mn-9Ni-5Mo-Cr alloys, which act as sinks of manganese and titanium in the matrices. This resulted in the reduction of the alloying elements concentration in the matrix, which is followed by the reduction in the segregation level of the elements at prior austenite grain boundaries, and consequently enhanced intergranular fracture strength. The optimum combination of strength and ductility was obtained in the Fe-5Mn-9Ni-5Mo-3Cr-l.5Ti alloy aged at 520°C for 2 hr. and was σ_{0 2}=1721 MPa, σ_LS=1756 MPa. and ε,= 10.2%.     

Influence of Zr content on microstructure and mechanical properties of implant Ti–35Nb–4Sn–6Mo–xZr alloys

The influence of Zr content on the microstructure and mechanical properties of implant Ti–35Nb–4Sn–6Mo–xZr (x=0, 3, 6, 9, 12, 15; mass fraction) alloys was investigated. It is shown that Ti–35Nb–4Sn–6Mo–xZr alloys appear to have equiaxed single β microstructure after solution treatment at 1023 K. It is found that the grains are refined first and then coarsened with the increase of Zr content. It is also found that Zr element added to titanium alloys has both the solution strengthening and fine-grain strengthening effect, and affects the lattice parameters. With increasing the Zr content of the alloys, the strength increases, the elongation decreases, whereas the elastic modulus firstly increases and then decreases. The mechanical properties of Ti–35Nb–4Sn–6Mo–9Zr alloy are as follows: σ_b=785 MPa, δ=11%, E=68 GPa, which is more suitable for acting as human implant materials compared to the traditional implant Ti–6Al–4V alloy.     

<Emphasis Type="Italic">An evaluation of</Emphasis> maraging steel sheet

Results of investigations into the metallurgical and mechanical behavior of 18Ni-9Co-5Mo maraging steel—one of a series of tough, high-strength alloys in a period of rapid development.     

Effect of secondary carbides addition on the microstructure and mechanical properties of (Ti, W, Mo, V)(C, N)-based cermets

(Ti, W, Mo, V)(C, N)-based cermets were prepared by mixing Mo₂C, WC and TaC with ultrafine (Ti, W, Mo, V)(C, N) powders, and then processed via a conventional P/M technique. The effect of Mo₂C, WC and TaC on the microstructure and mechanical properties of (Ti, W, Mo, V)(C, N)-8 wt.% Ni-7 wt.% Co systems was investigated. The Mo₂C content was varied from 0 to 10 wt.% and additive WC or TaC was added at a level of 5 wt.% with Mo₂C addition. The results show that the densification of (Ti, W, Mo, V)(C, N)-8 wt.% Ni-7 wt.% Co cermets was improved significantly by the addition of Mo₂C. With the increase of Mo₂C content, there is a coarsening tendency in the microstructure of (Ti, 20W, 15Mo, 0.2V)(C, N)-8Ni-7Co system, but the refinement for (Ti, 15W, 5Mo, 0.2V)(C, N)-8Ni-7Co. TaC addition decreases the density of (Ti, 15W, 5Mo, 0.2V)(C, N)-10Mo₂C-8Ni-7Co cermet and thus weakens its bending strength. (Ti, 15W, 5Mo, 0.2V)(C, N)-10Mo₂C-5WC-8Ni-7Co cermet has optimal mechanical properties: bending strength of 1999 MPa, hardness (H_v) of 1677 MPa and toughness of 9.95 MPa m^1/2 respectively by adding WC, which is due to its ultrafine and weak core/rim structure.     

Effect of tungsten and gallium on the structure and magnetic and mechanical properties of Fe-Cr-Co alloys

Effects of the alloying additions of W and Ga, cold deformation, and regimes of heat treatment on the magnetic and mechanical properties of precipitation-hardening Fe-Cr-Co alloys have been investigated. It has been shown that the alloying with tungsten leads to a strengthening of the α solid solution and an additional jumplike increase in strength after deformation and age hardening. The coercive force grows simultaneously with an increase in strength; the structure of the alloy in this case contains a large concentration of linear defects (dislocations), which indicates an important contribution of magnetoelastic energy to the formation of the high-coercivity state and of elastic strains to the increase in the strength properties. The character of fracture becomes brittle. The modifying of the alloy with gallium leads to an increase in plasticity due to the dispersion of the structure, formation of retained austenite in it, and formation of an interphase layer more uniform in composition. The character of fracture changes from brittle to brittle-ductile. A high-strength magnetically hard material has been obtained with H _c = 90–125 A/cm, σ _m = 120–130 G cm³/g, B _r = 0.6–0.65 T, σ_0.2 = 1300–1600 MPa, and δ = 2.0–4.6%.     

Effects of Mg content on microstructure and mechanical properties of low Zn-containing Al−xMg−3Zn−1Cu cast alloys

Effects of Mg content on the microstructure and mechanical properties of low Zn-containing Al?xMg? 3Zn?1Cu cast alloys (x=3?5, wt.%) were investigated. As Mg content increased in the as-cast alloys, the grains were refined due to enhanced growth restriction, and the formation of η-Mg(AlZnCu)₂ and S-Al₂CuMg phases was inhibited while the formation of T-Mg₃₂(AlZnCu)₄₉ phase was promoted when Mg content exceeded 4 wt.%. The increase of Mg content encumbered the solution kinetics by increasing the size of eutectic phase but accelerated and enhanced the age-hardening through expediting precipitation kinetics and elevating the number density of the precipitates. As Mg content increased, the yield strength and tensile strength of the as-cast, solution-treated and peak-aged alloys were severally improved, while the elongation of the alloys decreased. The tensile strength and elongation of the peak-aged Al?5Mg?3Zn?1Cu alloy exceed 500 MPa and 5%, respectively. Precipitation strengthening implemented by T′ precipitates is the predominant strengthening mechanism in the peak-aged alloys and is enhanced by increasing Mg content.     

Generalized model for atomic site preference in crystal and its application in rare-earth alloys

A generalized atomic site preference (ASP) model for crystalline compounds is developed. The ASP state can be characterized quantitatively by the atomic distribution tensor or the ASP tensor. The freedoms and the value ranges of the ASP state parameters are analyzed and determined. Based on the present model, the ASP behaviors of atom Al in LaNi_5?xAl_x with CaCu₅ structure and atom M in SmCo_12?xM_x (M = Mn or Mo) with ThMn₁₂ structure are simulated by a thermodynamic mean field method and the inversed pair potentials. The calculated results show (1) in LaNi_5?xAl_x, the site preference degree of Ni on sublattice g decreases with the increasing of Al composition, and all Al atoms occupy sublattice g preferentially; (2) Mn and Mo prefer to locate on sublattice i in SmCo_12?xM_x alloys. The present results agree well with the experimental results and/or the reported theoretical calculations in literature.     

Solid State Interaction in Ni-Mo-B System During Mechanical Alloying and Annealing

This work presents the results of a study of Ni_87?x Mo _x B₁₃ alloys (x?=?7, 10 and 14?at.%), which were obtained by mechanical alloying (MA) of elemental powder mixtures in a MAPF-2M high-energy planetary ball mill. The x-ray diffraction analysis and differential scanning calorimetry measurements were used. The single-phase fcc solid solutions of Mo and B in Ni were formed by MA of Ni-Mo-B mixtures of various compositions for 6-8?h. The coherent domain sizes of solid solutions calculated from the x-ray peak widths were 12-14?nm. The exothermic effects on the DSC curves, which corresponded to the phase transformations of supersaturated Ni(Mo,B) solid solutions, were observed during heating of the synthesized alloys. After heating to 700?°C, the alloys contained a fcc Ni(Mo) phase and a metastable hexagonal MoB₄ phase. Thermodynamically stable phase composition of Ni₈₀Mo₇B₁₃ and Ni₇₇Mo₁₀B₁₃ alloys, containing three phases: fcc Ni (Mo), Ni₂₁Mo₂B₆ with cubic lattice and Ni₃B with orthorhombic lattice, was reached after the isothermal annealing at 1000?°C. The ratio between the amounts of these phases in the alloys corresponds to their location in a three-phase area of the Ni-Mo-B equilibrium phase diagram.     

New ternary Yb5Sb3-type R5T1−x{Sb,Bi}2+x phases (R = Y,Dy, Ho,T = Co,Ru, Rh,Pd) and their magnetic properties

Several novel R₅T_1?x{Sb,Bi}_2+x phases having the Yb₅Sb₃-type structure (space group Pnma) have been synthesized. The cell parameters are: a = 1.20668(9), b = 0.88396(7), c = 0.78745(7) nm for Y₅CoSb₂; a = 1.19939(7), b = 0.88364(5), c = 0.78283(5) nm for Dy₅CoSb₂; a = 1.19633(8), b = 0.89231(6), c = 0.78450(6) nm for Ho₅RhSb₂; a = 1.18650(6), b = 0.90455(4), c = 0.79260(4) nm for Ho₅PdSb₂; a = 1.2215(3), b = 0.8948(2), c = 0.7977(2) nm for Y₅CoBi₂; a = 1.1781(8), b = 0.9071(7), c = 0.7936(6) nm for Tm₅Co_0.5Bi_2.5; a = 1.1972(1), b = 0.92096(9), c = 0.80048(9) nm for Ho₅RuBi₂; a = 1.2082(1), b = 0.90346(9), c = 0.79413(8) nm for Ho₅RhBi₂ and a = 1.20374(5), b = 0.91076(4), c = 0.80135(4) nm for Ho₅PdBi₂, respectively. Magnetization measurements indicate ferromagnetic transitions for Dy₅CoBi₂, Ho₅RhSb₂, Ho₅RhBi₂, Ho₅PdSb₂ and Ho₅PdBi₂ at T_C = 34, 38, 28, 42 and 38 K, respectively. The Ho₅RhSb₂ and Ho₅PdBi₂ compounds show additional magnetic transitions at about 18 K, probably associated with a spin reorientation. The magnetocaloric effect of Dy₅CoBi₂ in terms of the isothermal entropy change, ΔS_m, is ?6.2 J/(kg/K) at 38 K and in terms of the adiabatic temperature change, ΔT_ad, is 2.2 K for a 5 T field change.     

High-Temperature Compressive Properties of TiC-Added Mo-Si-B Alloys

High-temperature compressive properties of two TiC-added Mo-Si-B alloys with nominal compositions of Mo-5Si-10B-7.5TiC (70Mo alloy) and Mo-6.7Si-13.3B-7.5TiC (65Mo alloy) (at.%) were investigated. The alloys were composed of four constituent phases: Mo solid solution (Mo_ss), Mo₅SiB₂, (Mo,Ti)C, and (Mo,Ti)₂C. The primary phases of the 70Mo and 65Mo alloys were Mo_ss and T₂, respectively. The compressive deformability of the 65Mo alloy was significantly limited even at 1600°C because of the elongated, coarse primary T₂ phase, whereas the 70Mo alloy had good compressive deformability and a high strength in the test-temperature range of 1000–1600°C; the peak stresses were 1800 MPa at 1000°C, 1230 MPa at 1200°C, and 350 MPa at 1600°C. At and above 1200°C, the peak stress values were more than double those of Mo-6.7Si-7.9B, Ti-Zr-Mo, and Mo-Hf-C alloys. The plastic strain in the 70Mo alloy at temperatures lower than the ductile–brittle transition temperature of T₂ was generated by plastic deformation of not only Mo_ss but also of (Mo,Ti)C and (Mo,Ti)₂C. This work indicates that (Mo,Ti)C and (Mo,Ti)₂C play an important role in determining the high-temperature strength and deformation properties of TiC-added Mo-Si-B alloys.     

Corrosion properties of nickel free austenitic stainless steels in 0·5M H2SO4 and 0·5M H2SO4 plus 0·4M NaCl

Abstract

The corrosion behaviour of four nickel free austenitic stainless steels were investigated in 0·5M H₂SO₄ and 0·5M H₂SO₄ plus 0·4M NaCl solutions by means of potentiodynamic and potentiostatic anodic polarisation testing. The performances of the nickel free alloys are compared to those of an experimental intermediate nickel alloy (4%Ni) and a standard AISI 304 steel grade. Once passivity was reached all alloys displayed similar current densities i _p in 0·5M H₂SO₄, independent from alloying. Mo and Cu were shown to be beneficial in decreasing the active dissolution currents and i _crit values. The commercial AISI 304 steel displayed superior resistance to pit initiation during potentiodynamic testing, and AISI 304 steel displayed the highest E _pit value of all alloys tested. When tested potentiostatically the N and Mo alloyed nickel free alloys showed excellent resistance to pit initiation and growth. The dominant effect of N was associated with repassivation of incipient pits, while Mo appeared to act at an earlier stage, suppressing initiation.     

Electrochemical corrosion characteristics of ZrNi5−xCox alloys

The electrochemical corrosion behaviour of a series of ZrNi_5−xCo_x alloys with x=0-4 has been tested using potentiokinetic polarisation technique. The polarisation curves were measured in deaerated 0.5 M sulphate solutions with pH=0.2-7 and in strong alkaline solution of KOH (pH=15). It is shown that the presence of greater amounts of Co in the alloy (x?2) worsens the passivating properties of the alloy in acidified sulphate solutions. On the other hand, in strong alkaline solutions, both low- and high-cobalt alloys undergo stable passivation. The degree of Ni substitution by Co in the alloys does not generally affect the shape of cathodic polarisation curves.     

Interdiffusion in pseudobinary sections of Ni3Al–Co ternary system

Interdiffusion in Ni₃Al intermetallic alloyed by 0–19 at.% Co was studied in three pseudo-binary sections: c_Al=22, c_Co=3.5, and c_Co=16 (c in at.%). The experiments were carried out at temperatures between 1173 and 1473 K. An attempt was made to analyze the interdiffusion coefficient into intrinsic diffusivities of individual components. Since no detectable shift of tungsten inert markers was observed, it was concluded that the intrinsic diffusivities of element pairs with varying concentration (Al/Ni and Co/Ni) in respective pseudo-binary sections are approximately equal one to another. The interdiffusion in pseudo-binary alloys Al/Ni (c_Co=const.) runs slightly faster than that in pseudo-binary alloys Ni/Co (c_Al=const.). The relations between the measured interdiffusion coefficients in the Ni_3−xAlCo_x ordered γ′ phase agree well with literature data for the interdiffusion coefficients in both the ordered γ′ and γ′+Co phases and also for the disordered Al–Ni and Co–Ni solid solutions. They are qualitatively explained by mutual interaction between constituents and by their interaction with vacancies.     

Microstructure and creep behavior of directionally solidified TiAl-base alloys

Tensile creep tests were conducted on directionally solidified TiAl alloys to discern the effect of alloying and lamellar orientation. A seeding technique was used to align the TiAl/Ti₃Al lamellar structure parallel to the growth direction for alloys of Ti–47Al, Ti–46Al–0.5Si–0.5X (X=Re, W, Mo, and Cr), and Ti–46Al–1.5Mo–0.2C (at.%). Tensile creep tests were performed at 750 °C using applied stresses of 210 and 240 MPa. Aligning the lamellar microstructure greatly enhances the creep resistance which can further be improved by additional alloying.     

Ferromagnetic resonance study of reduced NiCl2 graphite intercalation compound

A commercial reduction compound of graphite intercalated with NiCl₂ has been investigated by FMR. The X-band measurements for 573 ? T ? 3.5 K and Q-band for 293 ? T ? 150 K show the presence of metallic Ni and some unreduced NiCl₂. The Ni resonance signals have very large linewidths, δH_pp ～ 1800 ? 2000 Oe for 300 ? T ? 150 K. Analysis of the lineshape indicates that Ni remains intercalated in the graphite. The intercalated Ni exhibits a Curie temperature which is approximately 50 K lower than that of bulk Ni. The NiCl₂ X-band signals observed for 150 ? T 3.7 K show a maximum in intensity and linewidth at about 15 K, which is attributed to thermally induced magnetic excitations in the remaining finite NiCl₂ clusters. An in-plane exchange constant, J/k = 15 K, is estimated for NiCl₂ from the temperature dependence of the signal intensity.     

Microstructure and Properties of Aluminum-Containing Refractory High-Entropy Alloys

A new metallurgical strategy, high-entropy alloying (HEA), was used to explore new composition and phase spaces in the development of new refractory alloys with reduced densities and improved properties. Combining Mo, Ta, and Hf with “low-density” refractory elements (Nb, V, and Zr) and with Ti and Al produced six new refractory HEAs with densities ranging from 6.9 g/cm³ to 9.1 g/cm³. Three alloys have single-phase disordered body-centered cubic (bcc) crystal structures and three other alloys contain two bcc nanophases with very close lattice parameters. The alloys have high hardness, in the range from H _v = 4.0 GPa to 5.8 GPa, and compression yield strength, σ _0.2 = 1280 MPa to 2035 MPa, depending on the composition. Some of these refractory HEAs show considerably improved high temperature strengths relative to advanced Ni-based superalloys. Compressive ductility of all the alloys is limited at room temperature, but it improves significantly at 800°C and 1000°C.     

Heat treatment of YuNDK3 5T5 Alloys

Conclusions We investigated the effect of the cooling rate from 900 to 600° and high-temperature magnetic tempering at 790–830° on the magnetic properties of YuNDK35T5 alloys.It was found that the magnetic properties remain substantially unchanged with changes of the cooling rate from 2.1 to 0.73 deg/sec. The optimal temperature and time of high-temperature magnetic tempering coincide with those of ITMT in a lead bath.Cooling in magnetic field at rates of 2.1–0.73 deg/sec with subsequent high-temperature magnetic tempering at 810° for 12 min and two-stage tempering at 650° for 6 h+550° for 24 h makes it possible to obtain the following magnetic properties of alloys YuNDK35T5 and YuNDK35T5BA without use of a lead bath; B_r=9250 G and 11,300 G; H_c=1470 Oe and 1410 Oe; (BH)_max=5.5·10⁶ G-Oe and 11.2·10⁶ G-Oe.Moscow Institute of Steel and Alloys. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 30–33, August, 1973.     

The thermal effect on magnetic properties of iron-containing coatings formed on titanium by plasma-electrolytic oxidation

The effect of annealing in air at T _an temperature up to 800°C on the magnetic characteristics, elemental and phase composition, and surface morphology of iron-containing oxide coatings on titanium is studied. Annealing at T _an ?? 500°C does not seem to affect the composition and morphology of coatings. The coercive force (H _c ) of specimens equals 70 Oe at room temperature and 256 Oe at 2 K. Upon annealing at 700 or 800°C, the H _c value decreases to 13 Oe. The change in the magnetic characteristics correlates with the crystallization of a number of iron and titanium phosphates, the redistribution of elements in the coatings and pores, and the surface formation of microcrystals and whiskers.     

Composition dependence on the martensitic structures of the Mn-rich NiMnGa alloys

The Mn-rich Ni₅₀Mn_25+xGa_25−x (x=0–5) alloys were developed to investigate the structural transitions and magnetic properties. Structural transitions from austenite to 5M, 7M, and non-modulated martensite were observed with the increase of Mn content. The lattice parameter a elongates, as where b and c contract, and the unit cell volume reduces with increasing Mn content. The martensitic transformation start temperatures M_s increase monotonically from 10.7 °C for x=2 to 102.7 °C for x=5. The saturation magnetization was measured at 5 K, where all the samples exhibit a martensitic structure. The average magnetic moments per Mn atom vary from 4.38 μ_B to 2.93 μ_B for x=0 to x=5. The negative effect of excess Mn atoms changes from −3.00 μ_B for x=2 to −7.25 μ_B for x=5. The excess Mn atoms modify the electronic structures of the unsubstituted Mn atoms, resulting in the sharp decrease of the magnetic moments of the unsubstituted Mn atoms with increasing Mn content. Structural incommensurability was observed with 7M for powder and non-modulated for bulk samper in a specific range of compositions and proved to be reversible when performing martensitic transformation. The 7M and non-modulated martensites Ni₅₀Mn₃₀Ga₂₀ possess similar saturation magnetizations and Curie temperatures. The non-modulated martensite was estimated to have a lower free energy than 7M, and should be more stable for a reverse martensitic transformation, leading to a higher austenite start temperature A_s, which is consistent with the experimental result.     

Effect of titanium on the kinetics of the σ-phase formation in a coarse-grained Fe–Cr alloy

The influence of titanium on the kinetics of the σ-phase formation promoted by an isothermal annealing at T=973 K was studied in coarse-grained quasi-equiatomic Fe–Cr alloys by using the ⁵⁷Fe Mössbauer Spectroscopy. It was found that the kinetics could be well-described in terms of the Johnson–Avrami–Mehl equation. The addition of titanium (up to 3 at%) was revealed to effect the transformation kinetics in the following way: for x_Ti⩽1.5 at%, its presence accelerates the process with the highest transformation rate for x_Ti=0.3 at%, for x_Ti⩾1.5 at%, titanium retards the formation of the σ-phase. Quantitatively, the effect of titanium on the kinetics was described in terms of a change of the effective activation energy.