Combined Addition Of Cr Research Articles

Tuning the hydride stability of the TiVNb-based alloys by equimolar Cr/Al addition

Body-centered multi-principal element alloys (BCC-MPEAs) based only on hydride-forming elements have low equilibrium plateau pressures during reaction with hydrogen and, consequently, high decomposition temperatures due to the high thermodynamic stability of related hydrides. In this work, we present a strategy to decrease the stability of the final hydrides formed in the BCC TiVNb alloy by simultaneous addition of two non-hydride forming elements, Cr and Al. The (TiVNb)100-x(CrAl)x alloys with x = 10, 20, 30, and 40 at.% crystallize as major BCC solid solutions with dendritic microstructures. Pressure-Composition-Temperature diagrams revealed that the combined addition of Cr and Al thermodynamically destabilizes the dihydride formation for x = 10 and 20 at.%. For higher Cr/Al contents the destabilization is too large to form stable hydrides under maximum 100 bar pressure. The absorption/desorption plateau pressure at room temperature for (TiVNb)80(CrAl)20 alloy are 9 and 0.6 bar, respectively, enabling a reversible capacity of about 0.8 H/M (1.4 wt%) at ambient conditions. The present results provide important insights into the effects of simultaneous Cr and Al additions in BCC-MPEAs and shed light on the design of new alloys with hydrogen absorption and desorption ability at ambient conditions.

The gradual disappearance of yield plateau in Zr–Sn–Nb–Fe–Mo alloy by the trace addition of Cr and V

Trace chromium (Cr, 0.1 wt. %) and vanadium (V, 0.05 wt. %) were doped to the Zr–Sn–Nb–Fe–Mo alloy (denoted as Zir) to investigate the tensile properties at room temperature. A clear yield plateau was observed in Zir alloy, while the yield plateau was gradually disappeared by the addition of Cr to Zir alloy (denoted as Zir-0.1Cr) and by the combined addition of Cr and V to Zir alloy (denoted as Zir-0.1Cr-0.05 V). Microscopic characterization results revealed that doping of Cr and V retarded the re-crystallization process in Zir alloy. Firstly, the mean grain size of matrix was reduced from 1.9 μm to 1.7 μm and 1.5 μm by addition of 0.1% Cr and 0.1% Cr + 0.05% V to Zir alloy, respectively. The fraction of low angle grain boundaries (LAGBs) increased from 50.2% to 53.9% and 60.8% in Zir-0.1Cr and Zir-0.1Cr-0.05 V, respectively. Secondly, the volume fraction of second phase particles (SPPs) increased from 7.2% to 11.1% and 11.8% in Cr-containing and Cr + V-containing alloys, respectively. The mechanism of yield plateau in our alloy was explained by the impurity-dislocation interaction and dislocation multiplication mechanism, and the gradual disappearance of yield plateau behavior at the early stage of yielding could be attributed to the gradual increment of mobile dislocation density in Zir-0.1Cr and Zir-0.1Cr-0.05 V alloys. The tensile tests with different pre-strains proved that the gradual disappearance of yield plateau was caused by the increase of mobile dislocations with increasing pre-strain.

Age Hardening and Microstructure of ZA84 Magnesium Alloy with the Combined Addition of Cr and Bi

The age hardening and microstructure of ZA84 magnesium alloy with the combined addition of Cr and Bi was studied by SEM and HRTEM. The results show that a trace amount of Cr and Bi has a significant enhancement effect on the hardness of aging. When the ZA84-0.2Cr-0.5Bi alloy was aged at 160 °C, during the early aging period, the matrix has serious lattice distortion and a large number of crystal defects. The microstructure at the peak aging consists of a large number of rod-like or blocky β′ 1 -MgZn 2 phases and granular Bi 2 Mg 3 phases, and the peak hardness HV value is 924.8 MPa. When ageing proceed, the precipitates coarsening results in the hardness value reduction.

The Effects of Cr and Al Addition on Transformation and Properties in Low‐Carbon Bainitic Steels

Three low‐carbon bainitic steels were designed to investigate the effects of Cr and Al addition on bainitic transformation, microstructures, and properties by metallographic method and dilatometry. The results show that compared with the base steel without Cr and Al addition, only Cr addition is effective for improving the strength of low‐carbon bainitic steel by increasing the amount of bainite. However, compared with the base steel, combined addition of Cr and Al has no significant effect on bainitic transformation and properties. In Cr‐bearing steel, Al addition accelerates initial bainitic transformation, but meanwhile reduces the final amount of bainitic transformation due to the formation of a high‐temperature transformation product such as ferrite. Consequently, the composite strengthening effect of Cr and Al addition is not effective compared with individual addition of Cr in low‐carbon bainitic steels. Therefore, in contrast to high‐carbon steels, bainitic transformation in Cr‐bearing low‐carbon bainitic steels can be finished in a short time, and Al should not be added because Al addition would result in lower mechanical properties.

Effects of Cr and Hf additions on the microstructure and properties of Nb silicide based ultrahigh temperature alloys

Four Nb silicide based ultrahigh temperature alloys with compositions of Nb–22Ti–16Si–3Al–2B–xHf–yCr ((x, y)=(0, 0), (0, 5), (4, 0) and (4, 5)) (at%) were prepared by vacuum non-consumable arc melting. The effects of Cr and Hf additions on the phase selection, microstructure, room-temperature fracture toughness and oxidation resistance at 1250°C of the alloys have been investigated. The results show that all the four alloys are comprised of primary silicides and Nbss dendrites together with one or two types of eutectic. The Cr addition does not change the crystal structures of 5-3 silicides but imposes a significant influence on the amount, size and morphology of the constituent phases. The Hf addition suppresses the formation of α(Nb,X)5Si3 but promotes the formation of γ(Nb,X)5Si3. The combined additions of Cr and Hf also cause the formation of Cr2(Nb,X) containing three-phase eutectic. The room-temperature fracture toughness of the alloys decreases with Cr addition while increases with Hf addition. The oxidation-resistant performance of the alloys has been ameliorated by Cr addition, while it has been significantly degraded by Hf addition in the absence of Cr. Furthermore, the formation mechanism of the scale has been illustrated.

High temperature oxidation resistance of cluster model designed alloys Cu-Cu12-[Mx/(12+x)Ni12/(12+x)]5 (M=Si, Cr, Cr+Fe)

Based on the stable solid solution cluster model, cupronickel is microalloylized in this paper. Alloys with different Ni-M (M=Si, Cr, Cr+Fe) ratios are designed at constant atomic ration of Cu (72.22 at.%). The high temperature oxidation resistance and mechanism of alloy are also investigated. In the Cu-Ni-Si system, the addition of Ni-Si can enhance the oxidation resistance of the alloy from two aspects: firstly, the Ni-Si is in solid solution state when being added as a cluster, it can inhibit the chemical reactivity of Cu-Ni-Si alloy; secondly, anti-oxidation precipitation can be obtained with the increase of Si/Ni ratio. Therefore, the oxidation resistance of the alloy is not because of the formation of the compact silicon oxide film. In the Cu-Ni-Cr system, the oxidation is obviously inhibited at medium temperatures (lower than 800 ℃). But at higher temperatures, the oxidation resistance is relevant to the integrality of chrome oxide layer. The high temperature oxidation resistance is closely related to Cr/Ni ratio, hence an appropriate Cr/Ni ratio is necessary for the good high temperature oxidation resistance. Compared with the third element Cr, the forth element Fe cannot be oxidized first. Therefore, combined addition of Cr and Fe can only inhibit the medium temperature oxidation, but not high temperature oxidation.

Effect of Molybdenum and Chromium Addition on the Susceptibility to Sulfide Stress Cracking of High-Strength, Low-Alloy Steels

Abstract The purpose of this study is to elucidate the effect of Mo and Cr addition on corrosion and sulfide stress cracking (SSC) of high-strength, low-alloy (HSLA) linepipe steel. Six hot-rolled API X70/X80 grade steel plates containing 0.04 wt% C with different amounts of Mo and Cr (0.2, 0.3 wt% Mo, 0.15, 0.3 wt% Cr, 0.1 wt% Mo-0.3 wt% Cr, 0.2 wt% Mo-0.3 wt% Cr) were prepared by identical thermomechanically controlled processes (TMCPs). The SSC of the tested steels was investigated in terms of microstructure, mechanical properties, and electrochemical properties such as corrosion resistance and hydrogen permeation. A single addition of 0.3 wt% Mo or a combined addition of Cr and Mo increased SSC resistance of the steels by modifying the microstructure from ferrite to acicular ferrite (AF) and secondary phases from grain boundary iron carbides to SSC-resistant degenerated pearlite or small martensite/austenite (M/A) constituents. A single addition of Cr increased the local corrosion of steels under exte...

Enhanced magnetocaloric response in Cr∕Mo containing Nanoperm-type amorphous alloys

The magnetocaloric effect of Fe76Cr8−xMoxCu1B15 (x=0,4) alloys is studied. Although the combined addition of Cr and Mo is more efficient in tuning the Curie temperature of the alloy, the Mo-free alloy presents a higher magnetocaloric response. The refrigerant capacity (RC) for the Mo-containing alloy is comparable to that of Gd5Ge1.9Si2Fe0.1 (for a field of 50kOe, RC=273Jkg−1 for the Mo alloy vs 240Jkg−1 for the Gd-based one), with a larger temperature span of the optimal refrigeration cycle (250K vs 90K, respectively). The restriction of the temperature span to 90K gives RC=187Jkg−1 for the Mo alloy. A master curve behavior for the magnetic entropy change is also evidenced.

Magnetic properties and microstructure of Fe 3B/Pr 2Fe 14B-type nanocomposite magnets with Co and Cr additions

Magnetic properties and microstructures of Fe 3B/Pr 2Fe 14B-type nanocomposite magnets have been studied. Increasing content of Pr enhanced the coercivity at the expense of remanence and magnetic energy products in Pr 4+ x Fe 78− x B 18 and Pr 4+ x Fe 76− x Cr 2B 18 ( x = 0 , 0.5, 1) alloys. Combined additions of Cr and Co further improved hard magnetic properties. Optimum magnetic properties for the Pr 4Fe 71Co 5Cr 2B 18 alloy with M r (∼1.31 T), H c (∼265 kA/m), (BH) max (∼115.4 kJ/m 3) and Pr 5Fe 70Co 5Cr 2B 18 alloy with M r (∼0.97 T), H c (∼385 kA/m), (BH) max (∼86.2 kJ/m 3) were obtained after the samples were annealed at 628 and 658 °C for 10 min, respectively. Partially replacing Pr by Tb improved the overall magnetic properties to M r (∼1.14 T), H c (∼439 kA/m), (BH) max (∼119.4 kJ/m 3) in Pr 4Tb 1Fe 70Co 5Cr 2B 18 alloy, and also reduced the optimum annealing temperature to 628 °C. Three-dimensional atom probe (3DAP) analysis showed that Cr is strongly partitioned in the Fe 3B soft phase and Co has higher content in the Pr 2Fe 14B hard phase.

Structure and 700 °C hot corrosion behavior of chromium modified platinum–aluminide coatings

It is well known that the addition of chromium to coatings on nickel‐base superalloys improves the hot corrosion resistance of the coating. Recognizing this advantage, the low‐temperature (700 °C) hot corrosion (LTHC) testing of chromium modified platinum aluminides was initiated in order to determine whether combined additions of Cr and Pt were even more beneficial. The substrates chosen were IN100 and IN738, two commercially used nickel‐base superalloys. It was found that the structure of the chromium modified platinum–aluminide coating was dependent on the sequence of modifying element addition. The optimum coating for LTHC resistance was obtained by the Cr–Pt–Al deposition sequence which resulted in a coating with a continuous PtAl2 layer on the surface backed up with a fairly high level of Cr and Pt.