4Cr 4Ti Alloy Research Articles

Quantum phase transition in Cr-Ti alloys

In this work we present the results of electrical resistivity and Hall coefficient measurements for antiferromagnetic Cr1−x−xat.Ti% alloys with 0 < x < 5.0. Our results show an abrupt jump in in density of carriers as a function of concentration of Ti at 2K, characterizing a quantum phase transition, with quantum critical point in xc=1.2at.Ti%.

Strain-rate sensitivity and fracture mode of V–5Cr–5Ti alloy

The strain-rate sensitivity of V–5Cr–5Ti alloy was investigated in the strain-rate range 10−4–10−1 s−1 at room temperature. The rate sensitivity decreased with the increase of plastic strain, which was qualitatively explained by dislocation thermal activation theory combined with a dislocation multiplication model. A modified Johnson–Cook model was developed to characterize the strain-rate dependence. Scanning electron microscopy of the fracture surfaces revealed that the dominant mechanisms of fracture were intergranular fracture and dimple rupture.

Laser remelting of Al 91Fe 4Cr 3Ti 2 quasicrystalline phase former alloy

In the present work, an Al–Fe–Cr–Ti alloy with adequate composition to form quasicrystalline phases has been surface remelted using laser processing techniques. The surface of spray formed Al 91Fe 4Cr 3Ti 2 bulk samples was remelted using a 2 kW CW Nd:YAG laser. Two different laser beam powers were applied with the goal of studying its influence in the quasicrystalline phase formation in the remelted coating. After laser treatment, the samples were characterized by X-ray diffractometry (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (FEG-SEM). The formation of quasicrystalline phases was observed in the X-ray diffractograms and their transformations were verified in DSC analyses. A greater formation of quasicrystalline phase was verified in the coating produced with smaller laser beam power, i.e. higher cooling rate, and its morphology was more close to the sphere. The results indicate the possibility of producing low density coatings containing quasicrystalline phases by laser remelting of spray formed materials.

Improving hydrogen storage properties of Laves phase related BCC solid solution alloy by SPS preparation method

Spark plasma sintering (SPS) is a newly developed technique for multiple-phase material preparation. In this article, a Laves phase related BCC solid solution V–Ti–Cr alloy was prepared by SPS method, and its microstructure and hydrogen storage properties were investigated and compared with those of the alloy prepared by arc melting method. The results indicated that the alloy prepared by SPS method possessed not only excellent activation and kinetics properties, but also a much larger hydrogen storage capacity. The maximum hydrogen storage capacity was determined to be 2.89 mass%, which is about 24% higher than that of the arc melting alloy, and the hydrogen desorption ratio was improved from 35% for the arc melting alloy to 60% for the SPS alloy. This was due to the absence of Laves formation elements in the BCC solid solution and the formation of the interface phase between the Laves phase and the BCC solid solution during the SPS process, which fully optimized the hydrogen storage property of the Laves phase related BCC solid solution alloy.

Electrochemical behavior of Ti–Cr alloys in artificial saliva

In this study, the corrosion behavior of commercially pure titanium (c.p. Ti), Ti–6Al–4V and five new experimental Ti–Cr alloys was evaluated through open-circuit potential (OCP) and potentiodynamic polarization measurement in an artificial saliva containing fluoride. Electron spectroscopy for chemical analysis (ESCA) was used to characterize the composition of the passive films on the alloy after potentiodynamic polarization measurement. It was found that in standard artificial saliva the OCP increases with higher Cr content in Ti–Cr alloys. In 0.5% NaF artificial saliva, the OCP decreases with decreasing Cr in Ti–Cr alloys, and all but Ti–5Cr remain consistently higher than those of c.p Ti and Ti–6Al–4V. Linear polarization results show that artificial saliva and artificial saliva containing 0.5% NaF result in different corrosion behavior in Ti–Cr alloys, c.p.Ti and Ti–6Al–4V. The Ti–Cr alloys had greater resistance to corrosion in the fluoride-containing artificial saliva than c.p. Ti and Ti–6Al–4V, respectively. ESCA results verify that after potentiodynamic polarization a passive film consisting of TiO 2 and Cr 2O 3 forms on the surface of Ti–Cr alloys. These experimental results show that the electrochemical corrosion behavior of Ti–Cr alloys in artificial saliva containing 0.5% NaF can be improved by increasing Cr content. This further indicates that Ti–Cr alloys could successfully be used for crown, bridge, and metal-ceramic restorations.

Hydrogen sorption properties of Ti–Cr alloys synthesized by ball milling and cold rolling

Three Ti–Cr alloys with nominal compositions of TiCr x ( x = 2, 1.8 and 1.5) were synthesized by cold rolling and ball milling of as-cast ingots, and their microstructures and hydrogenation properties were studied. X-ray diffraction showed that TiCr x transformed from a mixture of C14 and C15 Laves phases to a metastable BCC phase after 5 h of ball milling under argon. Cold rolling did not lead to the formation of a metastable BCC phase but only to the reduction of TiCr x size particles under 20 nm. Surprisingly, the hydrogen absorption/desorption curves of cold rolled and ball milled samples at 323 K were quite similar. This result proves that hydrogen storage properties do not depend only on microstructure and that cold rolling could be an interesting method to synthesize hydrogen storage materials.

Microstructural characterization of a laser remelted coating of Al 91Fe 4Cr 3Ti 2 quasicrystalline alloy

A bulk sample of Al–Fe–Cr–Ti alloy with adequate composition to form quasicrystalline phases has been surface remelted, using laser processing techniques, to produce a quasicrystalline surface coating. After the laser treatment, the samples were characterized by X-ray diffractometry, differential scanning calorimetry, scanning electron microscopy and scanning/transmission electron microscopy. The results indicate the feasibility of producing low-density coatings containing quasicrystalline phases by laser remelting on a bulk sample of an aluminum-based alloy.

An improved procedure for radiochemical processing of activated fusion-reactor-relevant V–Cr–Ti alloy

The most promising structural material for both demonstration and commercial fusion reactors with liquid metal coolants is vanadium–chromium–titanium (V–Cr–Ti) alloy. Since its base is expensive and scarce vanadium, it is desirable to return this material into fusion power engineering after the reactor decommissioning. This is feasible only after purification of the V–Cr–Ti alloy from activation products. We have developed extraction technology for reprocessing of the activated V–Cr–Ti alloy. Recycling of the alloy after such a reprocessing does not require shielding against ionizing radiation. The solution of di-2-ethyl-hexyl-phosphoric acid (D2EHPA) in a hydrocarbon thinner was chosen as an extraction solvent. The process flow sheet includes dissolution of the V–Cr–Ti alloy in a nitric acid, titanium extraction from a nitrate solution, vanadium extraction at pH 2.0–2.5 and chromium extraction at pH of 4.2–4.5. In previous studies parameters of the extraction processes were studied at static conditions. Experiments with extraction of vanadium and chromium performed in dynamic conditions have shown that maintenance of the necessary pH in a solution requires use of buffer systems (on basis of formate). Joint extraction of vanadium and chromium with required purification from the main activation products (Co-60 and Eu-152) appeared to be feasible using only one reagent.

Ti-Cr Nanoparticles Prepared by Electrical Wire Explosion

We previously proposed a new method to synthesize nano-sized powders of various alloys and intermetallic compounds. The method consisted of electrical wire explosion of electrodeposted metal wires. In this study, the method was applied for Ti-Cr alloy. The overall composition of the Cr-coated Ti wire was about Ti-25 at% Cr. The explosion products consisted of equilibrium phases of α-Ti and TiCr2 phases along with meta-stable Ti-rich β phase. The composition of β phase estimated from its lattice parameter was Ti-13 at% Cr. The β phase decomposed completely to α-Ti and TiCr2 phases during isothermal aging at 600°C for one day.

Conception of operation of in situ oxide coating as applied to V/Li blanket

Development of in situ insulating coating onto inner wall of ducts is a promising way to mitigate the MHD pressure drop concerning V/Li blanket. The interdependence between structure of oxygen-containing V–4Ti–4Cr alloy and durability of Er 2O 3 insulator coating during contact with Li[Er] melt were studied and summarized. It was revealed that the inner oxidizing zone containing TiO 2 precipitations and non-equilibrium defects formed in the V–4Ti–4Cr during pre-charging procedure provided the most efficient oxygen consumption for Er 2O 3 formation during contact of V-alloy with Li[Er]. The kinetic model of interaction of components in the V, Ti[O]–Li[Er] system is proposed.

Correlation between hydrogen distribution in V–4Cr–4Ti alloy and impact strength

Distribution of hydrogen isotopes was examined by tritium radioluminography using imaging plates for specimens of a V–4Cr–4Ti alloy prepared from two different plates fabricated with cold rolling under two different conditions (93% and 96% reduction in thickness) and recrystallization annealing. Influence of hydrogen on impact strength was also studied. Radioluminographs showed that tritium was concentrated in band-like regions where Ti(C,N,O) precipitates were densely distributed. The extent of tritium accumulation in the band-like regions and their shapes, however, were different between the two types of specimens; the band-like regions were thinner and more elongated, and the trapping effects of precipitates was smaller for the specimen prepared with higher extent of cold working. On the other hand, this type of specimen showed lower susceptibility to hydrogen embrittlement. These observations indicated that precipitate distribution prepared with higher extent of cold working is preferable to provide better durability against hydrogen embrittlement.

Corrosion mechanism of Ti–Cr alloys in solution containing fluoride

Objective The objective of this study was to clarify the influence of chromium content on surface reaction of Ti–Cr alloys in an acidic fluoride-containing saline solution. Methods Four Ti–Cr alloys containing 5, 10, 15 or 20 mass% chromium were characterized in terms of dissolution of metals in an acidic fluoride-containing saline solution and surface structure by X-ray photoelectron spectroscopy and Auger electron spectroscopy. Results Total amount of metals dissolved from each alloy decreased with increase in chromium content. The surface oxide films of Ti–Cr alloys before and after immersion in an acidic fluoride-containing saline solution consisted of titanic and chromic species, such as oxide, hydroxide, and hydrate. The [Cr]/([Ti] + [Cr]) ratio in the surface oxide film on as-polished Ti–Cr alloys was closely correlated with chromium content. However, the ratio in any alloy approximately doubled after immersion. Although thick oxide films were observed after immersion, all alloys showed a thinner oxide film than commercially pure titanium. Significant In all alloys, concentration of chromic species such as oxide and hydroxide in the surface oxide film was associated with chromium content, and chromic species improved corrosion resistance to fluoride.

Structure and grindability of dental Ti–Cr alloys

The purpose of this study was to investigate the structure and microhardness of a series of binary Ti–Cr alloys with Cr contents up to 30 wt%. In addition, the grindability was also evaluated using an electric dental handpiece with SiC wheels, with the goal of developing a titanium alloy with better mechanical properties and machinability than commercially pure titanium (c.p. Ti), a metal generally considered to be difficult to machine. This study evaluated the phase and structure of Ti–Cr alloys, using an X-ray diffraction (XRD) for phase analysis and optical microscope for microstructure of the etched alloys. Grindability was evaluated by measuring the amount of metal volume removed after grinding for 1 min. Results indicated that the structure of Ti–Cr alloys is sensitive to the Cr content. The cast c.p. Ti has a hexagonal α phase. With 5 wt% Cr, metastable β phase starts to be retained. With Cr contents higher than 10 wt%, the equi-axed β phase is almost entirely retained. In addition, athermal ω phase was found in the Ti–5Cr and Ti–10Cr alloys. The largest quantity of ω phase and highest microhardness were found in Ti–10Cr alloy. The grinding rate of the Ti–Cr alloys showed a similar tendency to the microhardness. The Ti–10Cr alloy exhibited the best grindability, especially at 1000 m/min, which presumably due to the brittle nature of the alloy containing the ω phase in the β matrix.

Magnetoresistance of ferromagneticCrxTi1−xNsolid solution nitride

${\text{Cr}}_{x}{\text{Ti}}_{1\ensuremath{-}x}\text{N}$ solid solution nitrides were prepared by nitridation of Cr-Ti alloys to measure their magnetic and transport properties. The experiment was motivated by calculations on magnetism pointing out similarities of CrN and ${\text{LaMnO}}_{3}$ (the parent compound of colossal magnetoresistance oxides). The bulk ${\text{Cr}}_{0.5}{\text{Ti}}_{0.5}\text{N}$ showed strong ferromagnetism $({T}_{c}\ensuremath{\sim}130\text{ }\text{K})$ while ferromagnetism was very weak for ${\text{Cr}}_{0.67}{\text{Ti}}_{0.33}\text{N}$, being consistent with our previous experimental results for epitaxial thin-film samples [Inumaru et al., Appl. Phys. Lett. 91, 152501 (2007)]. These results confirmed that the ferromagnetism is an intrinsic characteristic of the bulk alloy and cannot be ascribed to lattice strains due to the epitaxy of the films. ${\text{Cr}}_{0.5}{\text{Ti}}_{0.5}\text{N}$ showed magnetoresistance of approximately 5% at 5 T. The magnetoresistance was expressed well by a scaling function $\ensuremath{-}(\ensuremath{\rho}\ensuremath{-}{\ensuremath{\rho}}_{0})/{\ensuremath{\rho}}_{0}=C{(M/{M}_{s})}^{2}$, where $M$ and ${M}_{s}$ are the magnetization for a given magnetic field and saturated magnetization, respectively. The constant $C$ for the nitride was 0.14, which was much smaller than that for manganese oxides $(C\ensuremath{\sim}4)$.

Evaluation of low-fusing porcelain bonded to dental cast Ti–Cr alloys

The purpose of this study was to compare the bonding characteristics of titanium porcelain Duceratin bonded to Ti–Cr alloys and commercially pure titanium (c.p. Ti). In addition, the thermal expansion coefficient (CTE) of all Ti–Cr alloys and c.p. Ti was also evaluated. The experimental metals used for this study include c.p. Ti, Ti–5Cr, Ti–10Cr, Ti–20Cr, Ti–25Cr and Ti–30Cr alloys (in wt.%). This study evaluated the bond strengths between commercial titanium porcelain Duceratin and Ti–Cr alloys. All the Ti–Cr alloys were tested for the determination of CTE with a dilatometer operating from room temperature up to 650 °C at a heating rate of 5 °C/min. The bond strengths of all the Ti–Cr alloys were higher than that of c.p. Ti. With the exception of Ti–5Cr and Ti–10Cr alloys, the bond strengths of all the other Ti–Cr alloys exceeded the lower limit value in the DIN 13.927 standard for the three-point bending test (25 MPa). By contrast, c.p. Ti surface after debonding exhibited the least amount of retained porcelain on the metal surface, and a higher rate of adhesive bond failure. More traces of retained porcelain were observed on specimens that contained higher alloying elements, such as Ti–25Cr and Ti–30Cr alloys, attesting to a better mechanical performance. In addition, the CTE of the Ti–Cr alloys ranged from 10.0 × 10 −6/°C (Ti–10Cr) to 11.8 × 10 −6/°C (Ti–30Cr), and were higher than that for c.p. Ti (10.1 × 10 −6/°C).

Tribological Behavior of Ti3SiC2 Sliding Against Ni-based Alloys at Elevated Temperatures

The dry sliding behaviors of titanium silicon carbide (Ti3SiC2) against Ni–Cr and Ni–Cr–Ti alloys from ambient temperature up to 600 °C were investigated. The tribological performance of Ti3SiC2 depends largely on counterface materials. Fracture and pullout of Ti3SiC2 grains followed by mechanical mix led to poor tribological property for Ti3SiC2/Ni–Cr alloy tribo-pair. However, for Ti3SiC2/Ni–Cr–Ti alloy tribo-pair, the oxides film of Ti on Ni–Cr–Ti alloy was effective to reduce friction coefficient and enhance wear resistance.

Evaluation of low-fusing porcelain bonded to dental cast Ti–Zr alloys

Abstract The purpose of this study was to compare the bonding characteristics of titanium porcelain Duceratin bonded to Ti–Cr alloys and commercially pure titanium (c.p. Ti). In addition, the thermal expansion coefficient (CTE) of all Ti–Cr alloys and c.p. Ti was also evaluated. The experimental metals used for this study include c.p. Ti, Ti–5Cr, Ti–10Cr, Ti–20Cr, Ti–25Cr and Ti–30Cr alloys (in wt.%). This study evaluated the bond strengths between commercial titanium porcelain Duceratin and Ti–Cr alloys. All the Ti–Cr alloys were tested for the determination of CTE with a dilatometer operating from room temperature up to 650 °C at a heating rate of 5 °C/min. The bond strengths of all the Ti–Cr alloys were higher than that of c.p. Ti. With the exception of Ti–5Cr and Ti–10Cr alloys, the bond strengths of all the other Ti–Cr alloys exceeded the lower limit value in the DIN 13.927 standard for the three-point bending test (25 MPa). By contrast, c.p. Ti surface after debonding exhibited the least amount of retained porcelain on the metal surface, and a higher rate of adhesive bond failure. More traces of retained porcelain were observed on specimens that contained higher alloying elements, such as Ti–25Cr and Ti–30Cr alloys, attesting to a better mechanical performance. In addition, the CTE of the Ti–Cr alloys ranged from 10.0 × 10 −6 /°C (Ti–10Cr) to 11.8 × 10 −6 /°C (Ti–30Cr), and were higher than that for c.p. Ti (10.1 × 10 −6 /°C).

Magnetic phase diagrams of Cr–Ti alloys

The magnetic phase diagram of Cr– x at% Ti (0⩽ x⩽10.2) is revisited. The critical temperatures were obtained from electrical resistivity and magnetic susceptibility measurements. Our results show that the antiferromagnetic phase is suppressed for x=1.3. However, previous papers predicted that the antiferromagnetic phase only disappears for x=2.0. Our results show that above x=1.3 the residual resistivity as a function of Ti concentration presents a discontinuity in these values. This change of behavior is possibly associated with a structural phase transition or a quantum phase transition.

Mechanical properties and deformation behavior of cast binary Ti–Cr alloys

As-cast Ti–Cr alloys prepared by using a dental cast machine with Cr content ranging from 5 to 30 wt.% were investigated. The experimental results indicated that these alloys obviously had different deformation behavior with various amounts of Cr. The bending strength of the Ti–20Cr alloy was about 1.8 times greater than that for commercially pure titanium (c.p. Ti). The Ti–10Cr alloy had relatively higher bending strength, almost as much as the Ti–20Cr alloy. This property is believed to be a result of the strengthening effect of the ω phase. From SEM fractographs, the Ti–10Cr alloy was characterized by coarse cleavage facets in the fractured surface together with some terrace-type morphology. The Ti–20Cr exhibited ductile properties; however, alloys with other compositions did not exhibit such properties. In addition, the elastic recovery capability of the Ti–20Cr alloy was greater than that of c.p. Ti by as much as 460%. In the unetched optical micrographs, the surfaces of the Ti–20Cr alloy were covered with large number of slip bands, thereby showing that the deformation of the Ti–20Cr alloy was dominated by the slip of dislocations. By judging from the results of the mechanical properties and deformation behavior, Ti–20Cr is considered to be the most feasible alloy for prosthetic dental applications if other properties necessary for dental casting are obtained.

Effect of isothermal aging on phase constitution and mechanical properties of Ti–Cr alloys

In this study, the effect of isothermal aging on phase constitution and mechanical properties of Ti–Cr alloys was investigated by measurements of electrical resistivity and Vickers hardness, X-ray diffraction, optical and scanning electron microscope observations and tensile tests. The obtained results are as follows. In solution treated and quenched state (STQ), hexagonal martensite, α′ was identified at 3Cr and 5Cr alloys, whereas β phase was identified from 5Cr to 20Cr. In 7Cr and 10Cr, athermal ω was also identified. Maximum of HV appeared at 7Cr and then HV decreased with increase of Cr content up to 15Cr. Above 15Cr, HV slightly increased due to solution hardening by Cr addition. On isothermal aging, precipitation of the α phase was delayed by Cr addition. In STQed state, tensile strength is 961 MPa in 10Cr, 988 MPa in 13Cr and 967 MPa in 15Cr, respectively. Elongation is 27.1% in 10Cr, 26.8% in 13Cr and 23.9% in 15Cr, respectively. In 13Cr and 15Cr alloys, nominal stress-nominal strain curves showed work-softening phenomenon after yield stress, whereas S–S curve of 10Cr alloy did not show that phenomenon. In 1173 K−12 ks aged state, tensile specimens of 10Cr and 13Cr were broken with no elongation, while the specimen of 15Cr alloy was broken after about 5% in elongation. It is considered that the reason why aged 10Cr and 13Cr specimen show no elongation is due to precipitation of α.