Boron-free Alloys Research Articles

Influence of boron addition on microstructure and mechanical properties of medium-Mn advanced high-strength steel

This study investigates the effects of 0.12 wt% boron addition on the microstructure and mechanical properties of a Fe-0.08C-4.5Mn-2.5Cr–1Si medium-Mn steel in as-rolled conditions and after the intercritical annealing process. In the as-rolled conditions, boron addition increased the strength and reduced the alloy ductility. In as-hot rolled conditions, an ultimate tensile strength (UTS)/elongation of 1195 MPa/5.5% and 1008 MPa/7% was achieved in the boron-added and boron-free alloys, respectively. However, the effect of boron on the intercritically annealed specimens was diverse. The intercritical annealing had no tangible effect on the mechanical properties of the hot-rolled specimen. However, the intercritical annealing at 700 °C for 600 s led to a UTS/elongation of 1029 MPa/19.5% in the boron-added alloy, the highest UTS/elongation combination among all specimens. The formation of carbo-boride precipitates on lath boundaries of the boron-added alloy possibly locked the boundaries thereby a temper-resistant martensitic structure was attained. The lath structure of the annealed alloy caused an enhanced strength in the boron-added specimen. Nonetheless, in the boron-free alloy, martensite was normally tempered and a considerable reduction in the strength was observed.

Experimental and computational analysis of stacking fault energy in B-doped Fe50−XMn30Co10Cr10BX multi-principal elements alloys

The effect of boron doping in Fe50−XMn30Co10Cr10BX multi-component alloys on the resulting stacking fault energy has been experimentally and computationally assessed to understand the alloys' deformation mechanisms from structural and thermodynamic perspectives. Firstly, the fcc and hcp phases were identified together with stacking faults along their (110) planes using high-resolution transmission electron microscopy. At the same time, they were theoretically predicted through thermodynamic CALPHAD and ab initio calculations. The average stacking fault energy for the boron-free alloy was 23.9 ± 2.4 mJ/m2, suggesting that the deformation mechanisms relate to dislocation slip and deformation twinning. The average stacking fault energy for the highest boron content (5.4 at%) was 50.1 ± 14.1 mJ/m2, indicating dislocation glide as the possible deformation mechanism. The boron content in the solid solution was modelled. The modelling suggested that the presence of Cr-B, Mn-B and Fe-B bonds points towards forming (Cr,Fe)2B borides, which was experimentally confirmed. The borides, fcc phase stability, and the boron in solid solution contribute to increased stacking fault energy, preventing the motion of Shockley partial dislocations and influencing the ɛ-hcp martensitic transformation.

Simultaneously enhancing strength and ductility of multiprincipal-element soft magnetic alloys

Herein, a boron-containing soft magnetic alloy (Al1.5Co4Fe2Cr)98.8B1.2 was fabricated. Compared to the boron-free alloy Al1.5Co4Fe2Cr, the boron-containing alloy exhibited an excellent combination of soft magnetic properties with tailored mechanical properties, with 1.6-fold increment in yield strength, 3.8-fold increment in plasticity, and minimal decrement in saturation magnetization.

Fe-Al-Si-Type Iron Aluminides: On the Strengthening by Refractory Metals Borides.

The effect of boron addition into Fe–28Al–5Si–X (X = -, 2Mo, or 2Ti) on the structure and high-temperature yield stress was investigated. Generally, the alloying of binary Fe3Al-type iron aluminides by silicon significantly improves high-temperature mechanical properties by solid-solution strengthening. On the other hand, the workability and ductile properties at room or slightly elevated temperatures get worse with the increasing silicon content. Boron alloying together with titanium or molybdenum alloying is one of the ways to improve the workability of this type of alloy and, at the same time, ensure the formation of a sufficient amount of secondary phase particles required for effective strengthening. In this paper, the influence of 1 at. % of boron on high-temperature yield stress is evaluated in response to structural changes and compared with results obtained previously on the same type of alloy (Fe–28Al–5Si–2X, X= -, Mo, or Ti) but without boron alloying. It can be concluded that the network structure of borides of refractory metals formed due to boron alloying works more effectively for alloy hardening at higher temperatures than a mixture of silicides and carbides present in the boron-free alloy of the same composition.

Microstructure evolution and stress rupture properties of K4750 alloys with various B contents during long-term aging

The relationship among B content, microstructure evolution and stress rupture properties of K4750 alloy during long-term aging were investigated. After aging at 800 ℃ for 1000 h, the decomposition degree of MC carbides of K4750 alloys with 0B, 0.007 wt. % B and 0.010 wt. % B were basically identical, which indicated that B has no inhibition on MC carbide decomposition during long-term aging. The MC carbide decomposition was accompanied by the formation of M23C6 carbides and a small number of η phases, which was controlled by the outward diffusion of C and Ti combined with the inward diffusion of Ni and Cr from the γ matrix. In addition, M23C6 carbides in boron-free alloy were in continuous chain and needle-like η phases were precipitated near them, while M23C6 carbides in boron-containing alloys remained in granular distribution and no η phases precipitation around them. Adding B could delay the agglomeration and coarsening of M23C6 carbides during long-term aging, which was because the segregation of B at grain boundary retarded the diffusion of alloy elements, thus weakened the local fluctuation of chemical composition near grain boundary. The stress rupture samples of K4750 alloys with various B contents after aging at 800 ℃ for 1000 h were tested at 750 ℃/380 MPa. The results indicated that the stress rupture properties of boron-containing alloys were significantly better than that of boron-free alloy, which could be attributed to the increase of grain boundary cohesion strength and the optimization of M23C6 carbide distribution due to the addition of B.

Effect of trace boron on microstructural evolution and high temperature creep performance in Re-contianing single crystal superalloys

The effect of trace B on the microstructure and creep properties under 1100 °C/130 MPa in three single crystal superalloys with various levels of B (0, 0.01 and 0.02 wt %) additions was investigated. Compared with the boron-free alloy, the creep rupture life decreased slightly for the alloy with 0.01 wt % B, but dropped obviously for the 0.02 wt% B contained alloy. The low B addition had a slight effect on the main element compositions of γ/γ′ by the high precision atom probe tomography (APT) analysis and no significant change of γ/γ′ misfit was observed. However, the contents of Re, Mo, Cr in γ phase were decreased with the high B addition, resulting in the decrease of γ/γ′ misfit and increase of the spacing of γ/γ′ interfacial dislocation networks. Meanwhile, the residual (γ+γ′) eutectics and borides with a large volume fraction obviously decreased the creep rupture properties in the high B addition alloy. This study is helpful for understanding the boron's role of strengthening mechanism in high temperature creep of Ni-base single crystal superalloys.

Effect of boron addition on the microstructure and mechanical properties of K4750 nickel-based superalloy

The effect of boron addition at 0, 0.007 wt. % and 0.010 wt. % on the microstructure and mechanical properties of K4750 nickel-based superalloy was studied. The microstructure of the as-cast and heat-treated alloys was analyzed by SEM, EPMA, SIMS and TEM. Lamellar M5B3-type borides were observed in boron-containing as-cast alloys. After the full heat treatment, boron atoms released from the decomposition of M5B3 borides were segregated at grain boundaries, which inhibited the growth and agglomeration of M23C6 carbides. Therefore, the M23C6 carbides along grain boundaries were granular in boron-containing alloys, while those were continuous in boron-free alloys. The mechanical property analysis indicated that the addition of boron significantly improved the tensile ductility at room temperature and stress rupture properties at 750 ℃/430 MPa of K4750 alloy. The low tensile ductility at room temperature of 0B alloy was attributed to continuous M23C6 carbides leaded to stress concentration, which provided a favorable location for crack nucleation and propagation. The improvement of the stress rupture properties of boron-containing alloys was the result of the combination of boron segregation increased the cohesion of grain boundaries and granular M23C6 carbides suppressed the link-up and extension of micro-cracks.

High-temperature deformation behaviors of Ti–2Al–9.2Mo–2Fe alloy with boron

Hot deformation behaviors of Ti–2Al–9.2Mo–2Fe alloy with boron were investigated in a hot compression test at temperatures ranging from 850 to 1000 °C and strain rates ranging from 0.01 to 10.00 s−1. With strain rate decreasing and deformation temperature increasing, dynamic recrystallization (DRX) was promoted in both alloys. The nucleation mechanism of DRX involved grain boundary bulging and subgrain rotation. In case of deformation at low temperatures and high strain rates, the boron-free alloy only showed dynamic recovery (DRV) phenomenon. However, due to the particle-stimulated nucleation mechanism of recrystallization by TiB particles, the boron-containing alloy shows DRX at that condition. These DRX grain nuclei are formed by lattice rotation and subgrain growth from deformation zone in the initial grains, which are close to those of TiB particle. Moreover, the flow stress of the boron-containing alloy is lower than that of the boron-free alloy due to the grain refinement during hot deformation process.

Microstructure and mechanical properties of Fe-Al-Nb-B alloys

ABSTRACTDoping of Fe–Al–Nb alloys with boron results in precipitation of stable C14 Laves phase Nb(Fe,Al)2 instead of metastable Heusler phase Fe2AlNb as in case of the ternary system. The boron stimulated precipitation of the Laves phase leads to preferential precipitation of the Laves phase along grain boundaries and – with higher supersaturation of Nb in the Fe-Al matrix – to an even distribution of additional precipitates within the grains. Though these microstructures seem to be more favourable than in the boron-free alloys, which show an uneven distribution of rather large Laves phase precipitates, no marked strengthening effect by the Laves phase in the Fe–Al–Nb–B alloys is observed.

Tensile behavior of RAFM alloys after neutron irradiation of up to 16.3 dpa between 250 and 450 °C

Tensile specimen of steel EUROFER97 and other alloys on the basis of RAFM steels such, as OPTIFER and F82H alloys, and Ga3X were irradiated and post-examined during a neutron irradiation program of up to 16.3dpa between 250 and 450°C in the HFR (High Flux Reactor) in the Netherlands. These tensile results were compared with former irradiation programs, with lower neutron doses of up to 0.8 and 2.4dpa to quantify the difference in tensile strengthening. The average increase of tensile strength was in a range of 300MPa between 0.8 and 16.3dpa at temperatures of 250–300°C. This behavior can be correlated with irradiation-induced changes in the microstructure. Most of the hardening can be attributed to dislocation loops, point defects or small precipitates as observed in boron-free alloys as F82H mod. and EUROFER97. Whereas the hardening in boron-containing alloys OPTIFER alloys and Ga3X can be correlated in addition with the combination of helium bubbles. At the highest irradiation and test temperature at 450°C, all tensile data of all investigated materials were in the range of those of non-irradiated and irradiated material due to thermal aging effects.

The influence of boron content on the structural and electrochemical properties of the La15Fe77B8-type hydrogen storage alloy

La15Fe10−xNi70Mn5Bx (x = 0, 1, 1.5, 2, 3) hydrogen storage alloys are prepared using a vacuum induction-quenching furnace. A structure analysis shows that the boron-free alloy is composed of a La0.99Mn0.32Ni4.71 phase and an (Fe, Ni) phase and that the alloys containing boron consist of the La0.99Mn0.32Ni4.71, (Fe, Ni) and La3Ni13B2 phases. As the x increase, the parameter a of the La0.99Mn0.32Ni4.71 and La3Ni13B2 phases increases, while the c decreases. The relative abundance of the La3Ni13B2 phase and the gather degree of the (Fe, Ni) phase increase with increasing x. Electrochemical testing shows that the boron content has an unapparent effect on the alloy electrodes' activation property. The maximum discharge capacity of the alloy electrodes is stable (approximately 310 mAh g−1) when x increases from 0 to 2. The cycling capacity retention rate at the 50th cycle monotonically increases from 56.6% (x = 0) to 76.7% (x = 3). The high-rate dischargeability of the alloy electrodes first increases with increasing x from 0 to 1.5 and then decreases until x increases to 3. The HRD is controlled by the hydrogen diffusion rate in the bulk of the alloy (x = 0–1.5) and the charge-transfer reaction of hydrogen on the alloy electrode surface (x = 1.5–3).

Role of starting phase of boron on the mechanical alloying of FeNbB composition

Mechanical alloyed Fe75Nb10B15 systems, prepared with crystalline or commercial amorphous boron and a similar composition with the same Fe/Nb ratio but no boron, have been studied as a function of milling time in the aim of enhancing the homogenization of boron and determining its role on the mechanical alloying process. Neither boron addition nor boron phase used affect the developed microstructure at very early stages. After 4h milling at 350rpm, the formation of an amorphous phase was observed for boron containing compositions while for the boron-free alloy a supersaturated solid solution was found in the final microstructure. The alloy prepared using commercial amorphous boron showed a larger fraction of amorphous phase than that prepared using crystalline boron for the same milling time, suggesting that amorphous boron accelerates the formation of the amorphous phase during mechanical alloying.

Effect of heat treatment on microstructure and property of Fe‐Cr‐B alloy

AbstractIn this article, the effect of heat treatment in different quenching temperature on microstructure and hardness of Fe‐Cr‐B alloy was studied, by contrast with boron‐free Fe‐Cr alloy. The results indicated that microstructure of boron‐free Fe‐Cr alloy consisted of the martensite and a few (Cr, Fe)7C3 type carbide. The microstructures had no obvious change with the increase of quenching temperature, but its hardness increased from 51.5 HRC to 60.8 HRC. When boron element was added into the Fe‐Cr alloy, the netlike eutectic structure began to break and spheroidizing after quenching, in which the borocarbide turned into spherical groups and network Fe2B phase was broken. Moreover, the portion of martensite increased, and the amount of secondary carbide decreased, and the size of secondary carbide began to largen after quenching. When the quenching temperature reached 1100°C, secondary carbide particles dissolved in the matrix wholly. The hardness of Fe‐Cr‐B alloy increased with the increase of quenching temperature below 1050°C. The hardness of sample containing 2.0% B and quenching at 1050°C reached 66.7 HRC. The hardness of Fe‐Cr‐B alloy had no obvious change when quenching temperature continued to increase. After tempered at 200°C, the microstructure of Fe‐Cr‐B alloy had no significant change and its hardness had slight decrease. The hardness of sample containing 2.0% B tempered at 200°C reached 63.9 HRC.

Solidification and grain refinement in Ti45Al2Mn2Nb1B

The solidification process of Ti45Al2Mn2Nb1B (Ti4522-1B) was studied together with the baseline alloy Ti45Al2Mn2Nb (Ti4522) through directional solidification. Boron addition at 1 at% was found to have a strong limiting effect on beta dendrite growth, resulting much finer beta dendrites than in the boron-free alloy. Boron addition at that level was also found to have changed the orientation relationship of peritectic alpha with beta dendrites. The peritectic alpha has the Burgers orientation relationship with the beta dendrites in Ti4522 whilst is randomly oriented in Ti4522-1B. The peritectic alpha in Ti4522-1B was likely to be inoculated by boride precipitates at the beta/liquid interfaces. Formation of randomly oriented peritectic alpha during solidification, boride precipitate-induced randomly oriented alpha during beta-to-alpha transformation and fine beta dendrites contribute to grain refinement in Ti4522-1B.

Soft magnetic amorphous Fe–Zr–Si(Cu) boron-free alloys

Amorphous Fe 80Zr x Si 20− x− y Cu y boron-free alloys, in which boron was completely replaced by silicon as a glass forming element, have been prepared in the form of ribbons by using the melt quenching technique. X-ray diffraction and Mössbauer spectroscopy measurements revealed that the as-quenched ribbons with the compositions with x = 6–10 at.% and y = 0, 1 at.% are fully or predominantly amorphous. Differential scanning calorimetry (DSC) measurements allowed the estimation of crystallization temperatures of the amorphous alloys. Soft magnetic properties have been studied by the specialized rf-Mössbauer technique. Since the rf-collapse effect observed is very sensitive to the local anisotropy fields it was possible to evaluate the soft magnetic properties of the amorphous alloys studied. The rf-Mössbauer studies were accompanied by conventional measurements of hysteresis loops from which the magnetization and coercive fields were estimated. It was found that amorphous Fe–Zr–Si(Cu) alloys are magnetically very soft, comparable with those of the conventional amorphous B-containing Fe-based alloys.

Tensile Ductility of Cast TiAl Alloys

The microstructural characteristics and room temperature tensile ductility in some cast TiAl alloys were analyzed. It was found that grain refinement, either through Q&A treatment in boron-free alloys or through low dose of boron addition in beta solidifying alloys with lamellar microstructures, is not sufficient for good ductility. For cast alloys with convoluted microstructures and fine lamellar microstructures the orientation distribution of gamma grains/lamellar colonies plays an important role in controlling ductility. In those fine-grained alloys a highly random orientation distribution of gamma grains/lamellar colonies is essential to improvement in ductility.

Effects of B on the Microstructure and Oxidation Resistance of Nb-Ti-Si-based Ultrahigh-temperature Alloy

Nb-Ti-Si-based ultrahigh-temperature alloys concocted with boron ranging from 0 to 2 at% are prepared by arc-melting technology. The effects of adding boron on their as-melted microstructure and oxidation resistance are analyzed. The (Nb,Ti)ss, β-(Nb,Ti)5Si3 and γ-(Nb,Ti)5Si3 exist in Nb-22Ti-16Si-6Cr-3Al-4Hf alloy, while (Nb,Ti)ss, α-(Nb,Ti)5Si3 and γ-(Nb,Ti)5Si3 are present in Nb-22Ti-16Si-6Cr-3Al-4Hf-1B and Nb-22Ti-16Si-6Cr-3Al-4Hf-2B alloys. The oxidation of Nb-Ti-Si-based ultrahigh-temperature alloys is dominated by the diffusion of oxygen through (Nb,Ti)ss. Compared to boron-free alloys, the boron-containing alloys have significantly lower oxidation rate when oxidized at 1 200 °C for less than 50 h, but, for more than 50 h, their oxidation resistance deteriorates.

The effect of boron on the abrasive wear behavior of austenitic Fe-based hardfacing alloys

The effect of boron on the abrasive wear behavior of the austenitic Fe–Cr–C–Si–B hardfacing alloys was investigated with varying boron concentration. It was found that the abrasive wear resistance of the hardfacing alloys increased up to 50% compared to that of boron-free alloys with increasing boron concentration. The mechanism of the abrasive wear resistance changed at 0.6wt.% boron. Below 0.6wt.% boron concentration, the abrasive wear resistance was improved almost linearly and strain-induced martensitic transformation was considered as the controlling factor for improving the resistance. Above 0.6wt.% boron, it was observed that the primary borides started to precipitate. Further increase in boron concentration was not able to enhance the resistance due to the negligible change of primary borides’ size and volume fraction. With these results, it was concluded that two different effects of boron on the wear resistance of the austenitic Fe–Cr–C–Si–B hardfacing alloys existed depending on the boron concentration.

Beneficial Effects of Boron Addition into γ-TiAl Alloys

The beneficial effects of boron addition on microstructure transformations and mechanical properties of γ-TiAl alloys were investigated. Two growth mechanisms of boride (TiB2) in γ-TiAl alloy were confirmed, the curved flaky borides are products of irregular eutectic reaction growing coupled with matrix, while some faceted blocky borides in boron-rich alloy are primary TiB2 phase growing directly in melt. The core of flaky TiB2 is ultra-fine B2 phase and there has an orientation relationship [1210] TiB2//[001]B2, (1010) //(010)B2. In addition to the well-known grain refinement effect, boron addition can suppress the formation of metastable feathery and Widmastätten structure and broadens cooling-rate-range for the formation of fully lamellar structure, consequently, it improves thermal stability of the lamellar structure and accordingly prolongs the creep rupture life significantly. Another beneficial effect of boron addition is that boride can restrain discontinuous coarsening on lamellar grain boundary by pinning action and accelerates recrystallization of γ grain by introducing TiB2/matrix interfaces as nuclear sites during homogeneous treatment at 1150°C. Therefore, compared with boron-free alloy more homogeneous and refined near γ microstructure can be obtained in boron modified alloy.

Effects of rapid quenching on microstructures and electrochemical properties of La 0.7Mg 0.3Ni 2.55Co 0.45B x( x=0−0.2) hydrogen storage alloy

In order to improve the electrochemical performances of La-Mg-Ni based electrode alloys with PuNi 3-type structure, a trace of boron was added in La 0.7Mg 0.3Ni 2.55Co 0.45 alloy. The La 0.7Mg 0.3Ni 2.55Co 0.45(x=0, 0.05, 0.1, 0.15 and 0.2) alloys were prepared by casting and rapid quenching. The electrochemical performances and microstructures of the as-cast and quenched alloys were investigated. The effects of rapid quenching on the microstructures and electrochemical performances of the above alloys were investigated. The results show that the as-cast and quenched alloys are composed of (La, Mg)Ni 3 phase, LaNi 5 phase and LaNi 2 phase. A trace of the Ni 2B phase exists in the as-cast alloys containing boron, and the Ni 2B phase in the B-contained alloys nearly disappears after rapid quenching. Rapid quenching increases the amount of the LaNi 2 phase in the B-free alloy, but it decreases the amount of the LaNi 2 phase in the boron-containing alloys. The effects of rapid quenching on the capacities of the boron-containing and boron-free alloys are different. The capacity of the B-free alloy monotonously decreases with increasing quenching rate, whereas the capacities of the B-contained alloys have a maximum value with the change of the quenching rate. The rapid quenching can improve the stability of La-Mg-Ni based electrode alloy but lowers the discharge plateau voltage and decreases the plateau length. The effect of rapid quenching on the activation capabilities of the alloys was complicated.