Influence of Small Cr Addition on Thermal Stability and Magnetic Properties of Fe-Co-Zr-Nb-B Glassy Alloys

Fe62Cos-xCrxZr6Nb4B20 （x=0-4 at. pct） metallic glasses show high thermal stability with a maximum supercooled liquid region of about 84.8 K. The addition of 2 at. pct Cr causes the extension of the supercooled liquid region remarkably, leading to the enhancement of thermal stability and glass-forming ability. The crystallization of the Fe-based glassy alloys takes place through a single exothermic reaction, accompanying the precipitation of more than three kinds of crystallized phases such as α-Fe, Fe2Zr and ZrB2. The long-range atomic rearrangements required for the precipitation of the multiple crystalline phases seem to play an important role in the appearance of the large supercooled liquid region through the retardation of the crystallization reactions. The Fe-based alloys exhibit soft ferromagnetic properties. The saturation magnetization decreases with increasing Cr content while the saturated magnetostriction increases as a function of Cr content. There is no distinct change in the saturation magnetization and coercive force with annealing temperature below the crystallization temperature. The devitrification gives rise to a considerable enhancement in both as and He.

Microstructure, mechanical properties and toughening mechanism of directional Fe2B crystal in Fe-B alloy with trace Cr addition

Exploring the effective way to improve Fe2 B's toughness has always been the hot topic in the researches of Fe-B wear resistant alloys.In the present work,the effects of Cr on the microstructure,mechanical properties and lattice structure of directional Fe2 B have been investigated.The affecting mechanism of Cr addition has been discussed according to the experimental and first-principle calculation analysis.The results show Cr addition can improve the toughness of directional Fe2 B on the longitudinal sections perpendicular to(002) crystal plane,without sacrificing the hardness distinctly.The toughening mechanism by Cr substitution has been revealed:Cr addition enriches the electron density between the B atoms along [002] direction,contributing to the shrinkage of the bond length and the enhancement of the bond strength of B-B bonds.The obtained results provide insight into the intrinsic reason for toughening Fe2 B by Cr doping.

Effect of Cr on microstructure and oxidation behavior of TiAl-based alloy with high Nb

Three novel multi-microalloying TiAl-based alloys containing high Nb were designed and fabricated Thermogravimetric method was applied to investigate the influence of Cr on the oxidation behavior of high Nb TiAl alloy at 1,073 K for 200 h in laboratory air. The 2 at.% and 4 at.% Cr were added into the alloy,(respectivel named 2 Cr and 4 Cr compared to the Cr-free ternary alloy, 0 Cr alloy). The alloys' microstructure and compositio as well as the composition distribution of the oxidation scale were analyzed by means of Scanning Electro Microscopy(SEM), Energy Dispersive Spectroscopy(EDS), and X-Ray Diffractometry(XRD). The results show that the addition of Cr decreases the grain size of the Nb-TiAl alloy and leads to a transformation from a full lamellar structure to a nearly fully lamellar structure. When oxidized at 1,073 K for 200 h, the oxidized mass gai of the alloy increases with an increase in Cr addition amount in the first 100 h and decreases in the last 100 h With the increase of Cr content, the oxidation surface turns compact but uneven in morphology, which may affec the oxidation resistance of the alloy by increasing the peeling off risk of the oxidation layer at friction conditions.

Influence of Cr element on impact fracture process of ductile Ni-resistant alloyed iron at low temperature

In this study, in order to investigate the influence of Cr element on the impact fracture process of ductile Ni-resistant alloyed iron at low temperature, different contents of Cr element were added to ductile Ni-resistant(DNR) austenitic alloyed iron. The experimental results show that Cr addition can increase the hardness of the DNR alloyed iron, but it has an destructive effect on low-temperature impact properties. Through the analysis of the dynamic load and absorbed energy of samples with different Cr contents in the impact fracture process, and the comparison of the impact fracture process at room and low temperatures, it reveals that Cr addition into the DNR alloyed iron can facilitate the formation of the carbide mixture in Mn23C6 and Cr23C6 with homogeneous and discontinuous distribution. Meanwhile, Cr addition also can improve the the maximum dynamic load and crack initiation energy at low temperature, but has no obvious effect on the yield behavior of the DNR alloyed iron in the impact fracture process. Compared with the impact crack propagation process at room temperature, the metastable propagation energy at low temperature declines significantly with an increase in Cr content. This is because the micro-cracks that caused by the carbides weaken the matrix, resulting in the decline of impact crack propagation resistance. The fracture analysis results also show that the impact fracture mechanism gradually transforms from ductile to brittle with an increase in Cr content at low temperature. It explains that too much Cr addition can lead to brittle fracture even though the austenitic matrix has a good toughness at low temperature.

A new strengthening mechanism driven by disruptive shear and solute segregation during warm rolling in 1.4 GPa class 12.5 wt% Al added-FeMnC ultra-lightweight steel

Novel strengthening of Fe-29.1Mn-12.5Al-1.35C-4.95Cr steel achieved by warm rolling was investi-gated.The solution-treated steel consisted of aγ-matrix containing nano-sizedκ-carbide((Fe,Mn)_(3) AlC)and elongated prior ferrite,which was transformed into FeAl-type B2 and Fe_(3) Al-type D0_(3) phases.The solution-treated steel exhibited poor strain hardening owing to glide softening associated withκ-carbide shearing by dislocations.However,after warm rolling with a reduction ratio of 30%at 300℃,the yield and tensile strengths significantly increased from 917 to 1300 MPa and 1025 to 1419 MPa,respectively.The tensile test conducted at 300℃to simulate warm rolling exhibited serrated flows,indicating dy-namic strain aging(DSA).Atom probe tomography exhibited that the C atoms inκ-carbide were swept away along the slip direction by disruptive shear during rolling at 300℃.The swept C atoms along the slip direction interacted strongly with dislocations at 300℃,with repeated pinning and breakaway of dislocations from the C atoms.This contributed to significant strengthening owing to the formation of a solute-rich atmosphere after warm rolling.The results of the tensile tests at 300℃indicated that the de-gree of strengthening was proportional to the pre-strain level.Tensile strength of 1.4 GPa can be achieved with good ductility(17%elongation)by warm rolling.This novel warm-rolling strengthening method ex-pedites the potential application of Fe-29.1Mn-12.5Al-1.35C-4.95Cr as a 1.4 GPa class ultra-lightweight steel.