Grain structure effect on quench sensitivity of Al-Zn-Mg-Cu-Cr alloy

The effect of grain structure on quench sensitivity of an Al-Zn-Mg-Cu-Cr alloy was investigated by hardness testing, optical microscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and scanning transmission electron microscopy. The results show that with the decrease of quenching rate from 960 ℃/s to 2 ℃/s, the hardness after aging is decreased by about 33% for the homogenized and solution heat treated alloy（H-alloy） with large equiaxed grains and about 43% for the extruded and solution heat treated alloy（E-alloy） with elongated grains and subgrains. Cr-containing dispersoids make contribution to about 33% decrement in hardness of the H-alloy due to slow quenching; while in the E-alloy, the amount of（sub） grain boundaries is increased by about one order of magnitude, which leads to a further 10% decrement in hardness due to slow quenching and therefore higher quench sensitivity.

The influence of surface roughness and deformation on dechromization of a Cu-Cr alloy

In order to realize the dechromization of a Cu-Cr alloy in HCl solution, the influence of surface roughness and deformation on dechromization of the Cu-Cr alloy was studied by means of metallographic observation, TEM, SEM/EDX, and CH1660A electrochemical instrument. The results showed that the bigger the sample＇s deformation and surface roughness, the shorter the incubation time of dechromization of the Cu-Cr alloy, and the trend of dechromization increases. Simultaneously, the deformation can increase the dechromization rate, invite stress corrosion, and decrease the compactibifity of the microstructure of the dechromization layer. And yet the surface roughness does not obviously affect the dechromization rate and the compactibility of the dechromization layer.

Effect of Deformation and Aging Treatment on Electrical Conductivity of Cu-Cr Alloy

The effect of deformation and aging treatment on the electrical conductivity of Cu-Cr alloy was studied. The results show that deformation can reduce the electrical conductivity of Cu-Cr alloy, but deformation followed by optimum aging treatment can effectively improve the electrical conductivity of Cu-Cr alloy, under the condition of 0～70% deformation, and the electrical conductivity of Cu-Cr alloy by aging treatment increases and the aging time of obtaining much better electrical conductivity of Cu-Cr alloy decreases with increase in deformation quantity of Cu-Cr alloy. The best electrical conductivity of Cu-Cr alloy after deformation can be obtained by aging treatment at 500 ℃. And also the reasons for the variations of alloy's electrical conductivity and the function of adding RE were analyzed.

Friction and Wear Property of Cu-Cr Alloy

The friction and wear behaviors of the Cu-Cr alloy sliding against GCr15 steel at different loads and rotate speed conditions were evaluated, and the worn surface morphologies were observed on a scanning electron microscope. Results show that as loads and rotate speed increase, the wear loss weight increases, by comparison, the biggest friction coefficient of Cu-Cr alloy was obtained at load 100 N and rotate speed at 100 r·min-1 friction condition. Moreover, the dominant wear forms was plough wear.

Corrosion Behavior of Cu-Cr Alloy in 3.5% NaCl+NH_3 Solution

The corrosion behavior of Cu-Cr alloy in 3.5%NaCl+NH3 solution had been studied, and the influences of the concentration of NH3 on corrosion resistance discussed by means of Metallograph, XRD, SEM and electrochemical method. The results show that the Cu is easier to corrosion than Cr, and the corrosion rate increases with the increasing of the concentration of NH3, and deformation worsen the corrosion resistance of the alloy in such corrosive environment.

Oxidation of two-phase Cu-Cr alloys with different microstructures

The oxidation of PM Cu 50Cr, MA Cu 40Cr and MS Cu 40Cr alloys at 800 ℃ in 0.1 MPa O 2 was studied. The most important difference of their oxidation behaviors is the formation of an exclusive chromia scale on the surface of the MS Cu 40Cr alloy and a continuous chromia layer beneath an outer CuO layer corresponding MA Cu 40Cr alloy, while a complex scale composing of CuO, Cu 2O, Cu 2Cr 2O 4 and Cr 2O 3 formed on the PM Cu 50Cr alloy. This result implies that alloy microstructure affects their oxidation behaviors largely. Microcrystalline structure provides numerous diffusion paths for reactive component chromium, shorter diffusion distance and rapid dissolution of Cr riched second phase. All these favor the exclusive formation of the most stable oxide. [

Effect of Lanthanum and Yttrium on Microstructures of Cu-Cr alloys

Microstructures of Cu-based alloys (including CuO.8CrO.05La, CuO.8CrO.lLa, CuO.8CrO.4La, CuO.8CrO.05Y, CuO.8CrO.lY and CuO.8CrO.4Y) were studied by optical microscope, X-ray diffractometer, Scanning electron microscope and Energy-dispersive X-ray spectroscopy. The results show that La and Y refine the grains and change the distribution of microstructures of Cu-Cr alloys. The sizes of Cr particles are smaller in CuCrRE alloys than in CuCr alloy. In CuCrLa and CuCrY alloys, La and Y usually respectively exist as compounds of CugLa and Cu5Y. These compounds distribute in the grains with sphere shape and on the grain-boundaries with slice shape.

Liquid phase separation of Cu-Cr alloys during rapid cooling

The ribbons of Cu-Cr alloys with high Cr content (15%- 35%, mass fraction) were prepared by rapid solidification. The microstructures of solidified samples were analyzed by scanning electron microscopy and transmission electron microscopy. The results reveal that a representative liquid phase separation microstructures are observed in Cu75Cr25 ribbons solidified at a cooling rate of about 104K/s. The liquid phase separation is not restrained when the cooling rate is enhanced to about 107K/s. However, the size of Cr particles solidified from Cr-rich liquid or Cr-rich regions in alloy melts could be refined by increasing the cooling rates. The size of Cr particles increases with increasing Cr contents when the ribbons contain 15% to 35%Cr.

A Cu-Cr alloy with nano and microscale Cr particles produced in a water-cooled copper mold

Microstructures have profound effects on the hardness and strength of Cu-Cr alloys. The microstructures of a Cu-Cr alloy cast in a water-cooled copper mold were studied in the present work. The scanning electron microscopy （SEM） results show that there are the copper matrix saturated with chromium, spherical precipitates of chromium separated from liquid phase during cooling before the initiation of so- lidification, and a eutectic phase in grain boundary areas. To investigate the effect of age-hardening treatment on the microstructures and properties of the material, some samples were subsequently age-hardened in a salt bath and investigated by transmission electron microscopy （TEM）. The results show that coherent precipitates with the diameter of 11 nm are detectable in the samples before and after the age-hardening stage. Of course, the volume fraction of coherent precipitates is higher after the aging process.

Coherent strengthening of aging precipitation in rapidly solidified Cu-Cr alloy

A single-roller melt spinning method was used to preduce Cu-Cr microcrystalline alloy ribbons.Through proper aging treatment, the strength and hardness of the alloy were remarkably enhanced while the conductivity only had a minimal decrease. Grain refinement and coherent dispersion strengthening were proved to be the major factors contributing to the improvement of strength and hardness of the alloy after aging. The degree of coherent strengthening was almost identical with that calculated by Gerod equatbo. Compared with the solid solution quenched Cu-Cr alloy, the peak hardness was increased 2. 6 times, in which about 27% was attributed to the grain refinement and 73 %, in turn, provided by coherent strengthening due to aging precipitation. Neither the soid solution strengthening nor vacancy strengthening had detectable effect on the strength and hardness of the rapidly solidified Cu-Cr alloy.

Dechromisation of Cu-Cr alloy in acid solutions containing Cl^-

The phenomenon, characteristics and influence factors of dechromisation of a Cu-Cr alloy in acid solutions containing Cl^- were studied by means of metallographic observation, SEM/EDX, TEM and XRD. The mechanism of dechromisation of Cu-Cr alloy was discussed. The results show that dechromisation of the Cu-Cr alloy occurs at a certain temperature in solutions with H^+ and Cl^- simultaneously. The corrosion starts initially at the interfaces between Cu phase and Cr phase, then develops gradually into the centers of Cr phase. It is also revealed that dechromisation rates of the Cu-Cr alloy increase with increasing concentration of H^+ or Cl^-, and temperature of the solutions.

Effects of extrusion on chromium precipitation in Cu-Cr alloy

Cu Cr alloys containing Cr from 0.14% to 2.0% in mass were prepared as foils for TEM observation before and after being extruded. The results show that before extrusion, the spheroid or short bar chromium disperse in copper matrix of the Cu Cr alloy, and the relationship between Cu and Cr follows the Nishiyama Wasserman (NW) relationship, i.e. [110] Cu ∥ [001] Cr . After the Cu Cr alloy was extruded at 860 ℃, dark field image along (224) Cu clearly shows that there are precipitated chromium particles in copper matrix. However, the SADP comprises only (112) Cu zone.

Preparation of FeCoNi medium entropy alloy from Fe^(3+)-Co^(2+)-Ni^(2+)solution system

In recent years,medium entropy alloys have become a research hotspot due to their excellent physical and chemical performances.By controlling reasonable elemental composition and processing parameters,the medium entropy alloys can exhibit similar properties to high entropy alloys and have lower costs.In this paper,a FeCoNi medium entropy alloy precursor was prepared via sol-gel and coprecipitation methods,respectively,and FeCoNi medium entropy alloys were prepared by carbothermal and hydrogen reduction.The phases and magnetic properties of FeCoNi medium entropy alloy were investigated.Results showed that FeCoNi medium entropy alloy was produced by carbothermal and hydrogen reduction at 1500℃.Some carbon was detected in the FeCoNi medium entropy alloy prepared by carbothermal reduction.The alloy prepared by hydrogen reduction was uniform and showed a relatively high purity.Moreover,the hydrogen reduction product exhibited better saturation magnetization and lower coercivity.

Influence of introducing Zr,Ti,Nb and Ce elements on externally solidified crystals and mechanical properties of high-pressure die-casting Al–Si alloy

High pressure die casting(HPDC)AlSi10Mn Mg alloy castings are widely used in the automobile industry.Mg can optimize the mechanical properties of castings through heat treatment,while the release of thermal stress arouses the deformation of large integrated die-castings.Herein,the development of non-heat treatment Al alloys is becoming the hot topic.In addition,HPDC contains externally solidified crystals(ESCs),which are detrimental to the mechanical properties of castings.To achieve high strength and toughness of non-heat treatment die-casting Al-Si alloy,we used AlSi9Mn alloy as matrix with the introduction of Zr,Ti,Nb,and Ce.Their influences on ESCs and mechanical properties were systematically investigated through three-dimensional reconstruction and thermodynamic simulation.Our results reveal that the addition of Ti increased ESCs'size and porosity,while the introduction of Nb refined ESCs and decreased porosity.Meanwhile,large-sized Al_3(Zr,Ti)phases formed and degraded the mechanical properties.Subsequent introduction of Ce resulted in the poisoning effect and reduced mechanical properties.

Effects of the extrusion parameters on microstructure,texture and room temperature mechanical properties of extruded Mg-2.49Nd-1.82Gd-0.2Zn-0.2Zr alloy

Microstructure,texture,and mechanical properties of the extruded Mg-2.49Nd-1.82Gd-0.2Zn-0.2Zr alloy were investigated at different extrusion temperatures(260 and 320℃),extrusion ratios(10:1,15:1,and 30:1),and extrusion speeds(3 and 6 mm/s).The experimental results exhibited that the grain sizes after extrusion were much finer than that of the homogenized alloy,and the second phase showed streamline distribution along the extrusion direction(ED).With extrusion temperature increased from 260 to 320℃,the microstructure,texture,and mechanical properties of alloys changed slightly.The dynamic recrystallization(DRX)degree and grain sizes enhanced as the extrusion ratio increased from 10:1 to 30:1,and the strength gradually decreased but elongation(EL)increased.With the extrusion speed increased from 3 to 6 mm/s,the grain sizes and DRX degree increased significantly,and the samples presented the typical<2111>-<1123>rare-earth(RE)textures.The alloy extruded at 260℃ with extrusion ratio of 10:1 and extrusion speed of 3 mm/s showed the tensile yield strength(TYS)of 213 MPa and EL of 30.6%.After quantitatively analyzing the contribution of strengthening mechanisms,it was found that the grain boundary strengthening and dislocation strengthening played major roles among strengthening contributions.These results provide some guidelines for enlarging the industrial application of extruded Mg-RE alloy.

Study on the hydrogen absorption properties of a YGdTbDyHo rare-earth high-entropy alloy

This study investigated the microstructure and hydrogen absorption properties of a rare-earth high-entropy alloy(HEA),YGdTbDyHo.Results indicated that the YGdTbDyHo alloy had a microstructure of equiaxed grains,with the alloy elements distributed homogeneously.Upon hydrogen absorption,the phase structure of the HEA changed from a solid solution with an hexagonal-close-packed(HCP)structure to a high-entropy hydride with an faced-centered-cubic(FCC)structure without any secondary phase precipitated.The alloy demonstrated a maximum hydrogen storage capacity of 2.33 H/M(hydrogen atom/metal atom)at 723 K,with an enthalpy change(ΔH)of-141.09 kJ·mol^(-1)and an entropy change(ΔS)of-119.14 J·mol^(-1)·K^(-1).The kinetic mechanism of hydrogen absorption was hydride nucleation and growth,with an apparent activation energy(E_(a))of 20.90 kJ·mol^(-1).Without any activation,the YGdTbDyHo alloy could absorb hydrogen quickly(180 s at 923 K)with nearly no incubation period observed.The reason for the obtained value of 2.33 H/M was that the hydrogen atoms occupied both tetrahedral and octahedral interstices.These results demonstrate the potential application of HEAs as a high-capacity hydrogen storage material with a large H/M ratio,which can be used in the deuterium storage field.

Effects of trace calcium and strontium on microstructure and properties of Cu-Cr alloys

Cu-0.57Cr-0.01Ca and Cu-0.58Cr-0.01Sr(wt.%)alloys were fabricated and processed by thermo-mechanical treatment.Their mechanical and electrical properties and microstructure were investigated in detail and compared with those of a Cu-0.57Cr(wt.%)alloy.The results showed that the softening resistance of the Cu-Cr alloy was significantly improved by the additions of Ca and Sr elements.Compared with the Cu-Cr alloy,the deformation microstructure of the Cu-Cr-Ca and Cu-Cr-Sr alloys was more difficult to recrystallize at elevated temperatures,and the Cr precipitates in the Cu-Cr-Ca and Cu-Cr-Sr alloys were smaller in size and had an FCC structure at any given aging state.The high strengths of the Cu-Cr-Ca and Cu-Cr-Sr alloys were mainly attributed to the dislocation strengthening provided by high-density dislocations and the precipitate strengthening provided by fine Cr precipitates.First-principles calculation showed that the segregations of Ca and Sr atoms at interface between Cr precipitates and copper matrix were favorable in energetics.This segregation effectively hindered the growth of Cr precipitates and significantly enhanced the pinning effect on the motion of dislocations and subgrain boundaries,eventually leading to the improvement in the softening resistance of the Cu-Cr alloy.