Dispersion and reaction of TiB2 in liquid iron alloys

Abstract

The degree of reaction and dispersion achieved when TiB₂ powders are melted in contact with liquid iron based alloys has been assessed via a levitation dispersion test which had been developed earlier. Both Fe₂B and TiC were observed to form as a result of dissolution and reaction of TiB₂. The formation of TiC occurs during the reaction of commercial grade TiB₂ with liquid iron alloys containing as little as 0·08 wt-%C. The reaction of high purity TiB₂ with liquid iron alloys containing 0·24 wt-%C does not however lead to TiC formation. The formation of Fe₂B was observed for all conditions tested, owing to the effectively zero solubility of boron in solid iron. The TiB₂ remaining after dissolution and reaction was found to produce relatively good dispersions in the iron matrix and therefore additions of TiB₂ to liquid iron alloys may provide a means of producing Fe–TiB₂ composite materials. However, the brittle properties of Fe₂B will mean that, whereas such materials may be very hard, they are likely to lack toughness.

MST/1477     

Assessment of the reaction of SiC powders with iron-based alloys

The degree of reaction and dispersion achieved when SiC powders are brought into contact with liquid iron-based alloys has been assessed by a levitation dispersion test. SiC was found to react rapidly with molten iron matrices to form iron silicides and graphite. Attempts to generate protective TiC or Al₂O₃ coatings on SiC in situ in liquid iron proved unsuccessful; neither was precoating SiC and Ni and/or Cu successful in providing protection against molten iron alloys. Unprotected SiC also reacted readily with iron in the solid state (1000–1200 °C). Precoating with Ni, however, provides protection and prevents SiC dissolution and suicide formation during sintering at such temperatures.     

Interface interaction in the B4C/(Fe–B–C) system

The wetting behavior in the B₄C/(Fe–C–B) system was investigated in order to clarify the role of Fe additions on the sinterability of B₄C. Iron and its alloys with C and B react with the boron carbide substrate and form a reaction zone consisting of a fine mixture of FeB and graphite. The apparent contact angles are relatively low for the alloys with a moderate concentration of the boron and carbon and allow liquid phase sintering to occur in the B₄C–Fe mixtures. A dilatometric study of the sintering kinetics confirms that liquid phase sintering actually takes place and leads to improved mass transfer. A thermodynamic analysis of the ternary Fe–B–C system allows accounting for the experimental observations.     

Glass forming ability of Fe–Co–Zr–Nd–B alloys and bulk permanent magnets derived from amorphous precursor

The glass forming ability (GFA) and magnetic properties for Fe_48−x Co₂₇Zr₃Nd _x B₂₂ (x = 0–6) alloys were investigated. It was found that the proper addition of Nd (4–5 at.%) was very effective in improving GFA. The as-cast Fe₄₄Co₂₇Zr₃Nd₄B₂₂ and Fe₄₃Co₂₇Zr₃Nd₅B₂₂ alloys exhibited good soft magnetic behavior, while showed hard magnetic property after annealing at 760 °C for 10 min. Bulk permanent magnets were obtained from crystallization of amorphous alloys, which could provide a promising way for the bulk magnet produced by the simple process of copper mold casting and subsequent heat treatment.     

Effect of different reinforcements on composite-strengthening in aluminium

In the development of metal-matrix composites, reinforcements of aluminium and its alloys with ceramic materials has been pursued with keen interest for quite sometime now. However, a systematic comparison of the effect of different reinforcements in powder-processed aluminium and its alloys is not freely available in the published literature. This study examines the influence of SiC, TiC, TiB₂ and B₄C on the modulus and strength of pure aluminium. B₄C appears slightly superior as a reinforcement when comparing the effect of SiC, TiC, B₄C and TiB₂ on specific modulus and specific strength values of composites. However, TiC appears to be a more effective reinforcement, yielding the best modulus and strength values among those considered in this study. The differences in thermal expansion characteristics between aluminium and the reinforcements do not seem to explain this observation. The other advantage of TiC is that it is economically a more viable candidate as compared to B₄C and TiB₂ for reinforcing aluminium alloys. It is suggested that the superior effect of TiC as a reinforcement is probably related to the high integrity of the bond at the Al-TiC interface.     

Amorphous/crystalline Fe55Ni20Cu5P10Si5B5 composite produced by two-component melt–spinning

ABSTRACT

This work presents unique microstructure and thermal properties of the Fe₅₅Ni₂₀Cu₅P₁₀Si₅B₅ alloy produced by novel modification of the melt-spinning method, where two precursor alloys are simultaneously ejected i.e. Fe₄₀Ni₄₀P₁₀Si₅B₅ and Fe₇₀Cu₁₀P₁₀Si₅B₅, forming a composite ribbon. The investigation of melting the precursors by differential scanning calorimetry confirms the liquid miscibility of the Fe₇₀Cu₁₀P₁₀Si₅B₅ alloy. The two-component melt-spun composite obtained from the two alloys is compared to the alloys produced from a homogeneous liquid. The electron microscopy, X-ray diffraction and differential scanning calorimetry show different microstructure of the composite in comparison with the traditionally melt-spun alloys and our results reveal that the composite alloy inherits the thermal properties of the precursors.

This paper is part of a Thematic Issue on The Crystallographic Aspects of Metallic Alloys.     

Formation of nanocrystalline structure during electron irradiation induced crystallization in amorphous Fe-Zr-B alloys

Effect of electron irradiation on the crystallization and phase stability of Fe₈₈Zr₉B₃ and Fe₇₁Zr₉B₂₀ amorphous alloys was examined. Electron irradiation at an accelerated voltage of 2000 kV was performed at room temperature. The Fe₇₁Zr₉B₂₀ alloy showed a wide supercooled liquid region and the ΔT_x value was 71 K, while no glass transition was observed in Fe₈₈Zr₉B₃ alloy. The amorphous phase in Fe–Zr–B alloys was not stable under irradiation and crystallization from the amorphous phase was accelerated by the irradiation. Nanocrystalline structure composed of α-Fe and cubic-Fe₂Zr was formed in Fe₈₈Zr₉B₃ alloy by irradiation induced crystallization, while no nanoscale precipitates of intermetallic compounds were formed during annealing. In Fe₇₁Zr₉B₂₀ alloy, the formation of nanocrystalline precipitates was also confirmed by irradiation induced crystallization, although the formation of nanocrystalline structure had not been realized in high B concentration Fe–Zr–B alloys by annealing. These new results show that electron irradiation is effective in producing a new nanocrystalline structure.     

Synthesis of Fe–4.6?wt% B alloy via electro-deoxidation of mixed oxides

Fe–4.6 wt% B alloy was synthesized via electro-deoxidation of the mixed oxide precursor. The oxides, Fe₂O₃ and B₂O₃, mixed in suitable proportions were sintered at 900 °C yielding pellets with a two-phase structure; Fe₂O₃ and Fe₃BO₆. The sintered pellets, connected as cathode, were then electro-deoxidized in molten CaCl₂ or in CaCl₂–NaCl eutectic, against a graphite anode at 3.1 V. The electrolysis at 850 °C has successfully yielded a powder mixture of Fe and Fe₂B. Sequence of changes during the electrolysis was followed by interrupted experiments conducted at 850 °C. This has shown that iron is extracted quite early during the electrolysis through the depletion of oxygen from the starting oxide; Fe₂O₃, forming the other iron oxides in the process. Boron follows a more complicated route. Fe₃BO₆, the initial boron-bearing phase, was depleted in the early stages due to its reaction with molten salt. This gave rise to the formation of calcium borate. Boron was extracted from calcium borate in later stages of electrolysis, which appeared to have reacted in situ with the iron forming compound Fe₂B. An erratum to this article can be found at     

Wear resistance of austenite–TiC–graphite microstructures prepared by laser coating

Abstract

Cast iron was laser coated with a nickel based covered electrode. The cover material consisted of titanium, cobalt, carbon, rare earth, and slag forming powders. The laser coated layer included substantial amounts of austenite, some TiC particles, and nodular graphite, as well as small quantities of austenite–Fe₃C eutectic. Sliding wear tests were carried out to evaluate the wear properties of the microstructures. The effects of alloying elements and microstructures on wear resistance were investigated. The role of austenite during wear was particularly emphasised by experimental tests.     

Fe-Si-B amorphous alloys with high silicon concentration

Amorphous phase formation with good ductility has been found in Fe-Si-B ternary alloys with high silicon concentration using a melt-spinning technique. The formation range of these amorphous alloys is in the range 0 to 29 at % silicon and 5 to 26 at % boron, being much wider than the previously reported range (0 to 19 at % silicon and 10 to 26 at % boron). The crystallization temperature (T _x) and Vickers hardness (H _v) of the Fe-Si-B amorphous alloys containing more than 19 at % silicon increase significantly with increasing boron content, while the increase in silicon content causes a decrease inT _x andH _v. TheT _x andH _v of Fe₆₆Si₂₈B₆ alloy with the highest silicon concentration are 740 K and 500 DPN, respectively. The decreases inT _x andH _v with silicon content are interpreted owing to the increase in the contribution of the repulsive interaction between silicon and silicon against the attractive interactions between iron and silicon or boron. Furthermore, the silicon-rich amorphous phase has been found to crystallize by the almost simultaneous precipitation of the two equilibrium compounds of Fe₃Si and Fe₂B, Fe₂Si_0.4B_0.6 or Fe_4.9Si₂B.     

Effect of composition on the crystallization and magnetic properties of Fe–Co–Si–B–Nb amorphous alloys

The crystallization behavior and magnetic properties of Fe₆₂Co₁₀Si_15−x B_18−y Nb_{(x + y)−5} amorphous alloys with x = 0–5 and y = 0–5 were examined. Primary crystallization temperature of Fe₆₂Co₁₀Si_15−x B₁₃Nb _x and Fe₆₂Co₁₀Si₁₀B_18−y Nb _y alloys increased with the addition of Nb. The primary and secondary crystallization temperatures were well separated when the Nb content is above 4 at%. The alloys with 15–18 at% B showed a distinct supercooled region. The Nb addition decreased the Curie temperature as well as room temperature saturation magnetization. The glassy-type Fe₆₂Co₁₀Si₁₀B₁₈ alloy exhibited good soft magnetic properties as well as a supercooled liquid region of 39 K. The finding of the glassy-type Fe-based alloy without Nb element exhibiting high Bs above 1.4 T is promising for future use as a soft magnetic glass material.     

Structure and mechanical properties of TiB2/TiC – Ni composites fabricated by pulse plasma sintering method

TiB₂/TiC – Ni composites were synthesized starting from the powders of Ti, B₄C and Ni, using Pulse Plasma Sintering (PPS) method. Typically used one-step (1100?°C–10?min.) and novel double-step sintering processes (900?°C–10?min. +1100?°C–5?min.) were applied and compared. XRD studies showed that the composite obtained by double-step sintering consisted of TiB₂, TiC and Ni phases. For one-step processing additionally undesired Ni₃B and graphite were detected. SEM observations revealed dark-grey grains of TiB₂, light-grey grains of TiC (both around 25?µm in size) and Ni areas surrounded by TiC. The composites synthesized in one- and double-step processes revealed the hardness and relative density of 2335 HV5 (±110) and 97.8% and 2470 HV5 (±70) and 99.8%, respectively. Novel double-step sintering process allowed to avoid undesired phases (graphite, Ni₃B) and only TiB₂, TiC and Ni were present in the structure. Additionally it was possible to decrease the temperature of the process comparing to other fabrication methods.     

Effect of Cr-doping on crystallization sequence and magnetic properties of Fe3B/Nd2Fe14B nanocomposite permanent magnets

Crystallization sequence starting from Nd_xFe_{82 − x}B₁₈ and Nd_xFe_{79 − x}Cr₃B₁₈(x = 3.5 – 5.5 at%) amorphous alloys has been investigated using X-ray diffractometer. In the alloys with Nd concentration around 5 at%, the intermediate compound Nd₂Fe₂₃B₃ first crystallizes along with Fe₃B from the amorphous state. Then, the Nd₂Fe₂₃B₃ phase decomposes to form a mixture of Nd₂Fe₁₄B, Fe₃B and αFe for the Cr-bearing systems, whereas it breaks up into another mixture of αFe and NdFe₄B₄ for the Cr-free systems. Atom probe field ion microscopy analysis has revealed that Cr is preferentially partitioned into the Fe₃B phase during the crystallization process, which may stabilize the Fe₃B-containing mixture exhibited in the Cr-doped systems. We can conclude that a large fraction of Nd₂Fe₁₄B produced from the distinct decomposition scheme of the intermediate Nd₂Fe₂₃B₃ phase exhibited in the Cr-doped systems brings about the high coercivity materials.     

Carbon/ceramics composites — Preparation and properties

Fabrication methods for carbon/ceramics composites were established by using two different processes of hot-pressing and pressureless sintering without any binder phase. In the hot pressing method, some boron compounds were found to be an effective aid for sintering and graphitization of coke powder above 2000°C under some pressure. When the content of boron compound such as B₄C was high, graphite/B₄C composites could be fabricated. If some other ceramic powder such as NbC, TiC or TaC was mixed in addition to the B₄C, three component composites with graphite matrix could be obtained. In pressureless sintering method, raw coke carbon powder was ground for a long time to be transformed in to a sinterable and non-graphitizing-type carbon powder. From a mix of ceramic powders such as SiC or B₄C with the ground coke powder, the composites of carbon/SiC or carbon/SiC/B₄C systems could be fabricated by heat-treatment under normal pressure.Some properties of the graphite samples and carbon/ceramic composites were investigated. It was found that their mechanical properties were much better than those of conventional graphite samples and the resistance to oxidation and corrosion was also excellent. It is suggested that the composites could be applied as bearing or mechanical seals both for use in high temperature environments and as machine parts in contact with some molten metals.     

Fabrication of TiC/TiB/Ti3AlC2 phases reinforced coatings on Ti-6Al-4V substrate

Intermetallic matrix composite coatings reinforced by TiC, TiB₂, and Ti₃AlC₂ were fabricated by laser cladding the mixed power Ti, Al, and B₄C on the Ti-6Al-4V alloy. X-ray diffraction, scanning electron microscope, and energy dispersive spectroscopy were chosen to investigate the structures and morphologies of the coatings. Results showed that the coatings mainly consisted of the reinforcements of TiC, TiB₂, and Ti₃AlC₂ and the matrix of Ti₃Al, TiAl, TiAl₃, and α-Ti. The hardness and wear-resisting property of the prepared specimens of Ti-45Al-10B₄C and Ti-45Al-20B₄C were studied contrastively. It was found that the coating was metallurgical bonded to the Ti-6Al-4V substrate. The micro-hardness and dry sliding wear-resisting properties of the specimen of Ti-45Al-20B₄C were enhanced further. And the micro-hardness of Ti-45Al-20B₄C was from 900 HV_0.2 to 1225 HV_0.2. The wear-resisting property of Ti-45Al-20B₄C was four times as large as that of the Ti-6Al-4V alloys.     

Effects of Nd and B contents on the thermal stability of nanocomposite (Nd,Zr)2Fe14B/α-Fe magnets

The effects of Nd and B contents on the microstructure and thermal stability of nanocomposite (Nd,Zr)₂Fe₁₄B/α-Fe magnets have been investigated. It is shown that for Nd_xFe_93−xZr₁B₆ (x = 9–11) alloys, the volume fraction of Nd₂Fe₁₄B increases with increasing Nd content, and the sample with x = 10 exhibits the optimal microstructure and thermal stability. Though the room-temperature _iH_c of Nd₁₁Fe₈₂Zr₁B₆ sample is the highest, it decreases more rapidly than that of Nd₁₀Fe₈₃Zr₁B₆ as temperature increases, indicating the deterioration of the temperature coefficient β. For Nd₁₀Fe_89−yZr₁B_y (y = 5–8) alloys, the remanence and the temperature coefficient α deteriorate with increasing B content. The coercivity and the temperature coefficient β first improve with increasing B content, reaching the optimal values at y = 7, then deteriorate with further increasing B. Coarse grains and the Fe₃B phase are observed in the Nd₁₀Fe₈₁Zr₁B₈ alloy.     

The mechanism of thermal explosion (TE) synthesis of TiC-TiB2 particulate locally reinforced steel matrix composites from an Al-Ti-B4C system via a TE-casting route

TiC-TiB₂ particulate locally reinforced steel matrix composites were fabricated by a novel TE-casting route from an Al-Ti-B₄C system with various B₄C particle sizes. The formation mechanism of TiC and TiB₂ in the locally reinforced regions was investigated. The results showed that TiC and TiB₂ are formed and precipitated from Al-Ti-B-C melt resulting from the dissociation of B₄C into Al-Ti melt when the concentrations of B and C atoms in the Al-Ti-B-C melt become saturated. However, in the case of coarse B₄C powders (≥40 μm) used, the primary reaction in the Al-Ti-B-C melt is quite limited due to the poor dissociation of B₄C. The poured steel melt infiltrates into the primary reaction product and thus leads to the formation of Al-Fe-Ti-B-C melt, thanks to the favorable reaction of molten Fe with remnant B₄C, and then TiC and TiB₂ are further formed and precipitated from the saturated Al-Fe-Ti-B-C melt. The relationship between the mechanisms of thermal explosion (TE) synthesis of TiC and TiB₂ in the electric resistance furnace and during casting was proposed.     

Workability Behavior of Powder Metallurgy Carbide Reinforced Aluminum Composites During Hot Forging

Experimental study was conducted to assess the consequence of titanium carbide (TiC), molybdenum carbide (Mo₂C), iron carbide (Fe₃C), and tungsten carbide (WC) reinforcements on the composite aluminum compacts. The hot deformation of the carbide reinforce aluminum compacts, Al-2TiC, Al-2WC, Al-2Fe₃C, and Al-2Mo₂C, with aspect ratios of 0.4 and 0.6, was carried out and the workability behaviors of the same were determined. The effect of carbide reinforcement and preform geometry on the relative density, stress ratio, σ_θ/σ_eff, and formability ratio was studied.     

The effects of carbon on the magnetic properties of nanocrystalline Fe-based alloys

We investigate the magnetic properties of nanocrystalline Fe_73.5Cu₁M₃Si_13.5B₉ (M=Nb or Mo) alloys when C is substituted for B up to 2 at%. It is found that the permeability and coercivity deteriorate with the content of C in the case of both M=Nb and Mo. The saturation magnetization also deteriorates as C is substituted for B in the case of M=Mo but it improves linearly with the C content in the case of M=Nb. This increase in the saturation magnetization of the Fe-Cu-Nb-Si-B alloy with C addition can provide an opportunity to overcome one of the main disadvantages, low magnetic flux density, of the alloy. In the latter part of the work we also investigate the magnetic properties of Fe_76.5–y Cu₁Nb_y (Si_0.5B_0.4C_0.1)_22.5 (0y3) alloys, particular emphasis being given to the role of Nb in the presence of C. It is found that C may help Nb to suppress the growth of -Fe grains in the alloy.     

Crystallization of Fe-Si-B metallic glasses studied by X-ray synchrotron radiation

We have studied the crystallization kinetics of Fe_90-x Si _x B₁₀ amorphous alloys withx ranging from 7 to 21, by synchrotron X-ray radiation. Using energy- dispersive X-ray diffraction, the kinetics of the different crystalline phases evolving during isothermal annealing were followed. These crystalline phases were identified as precipitation of-Fe(Si) and/or Fe₃Si in the amorphous matrix. At a later time or at a higher temperature, Fe₂B starts to crystallize (x < 21 ). Only at low iron concentration (x = 21) was the second phase different, namely Fe₅SiB₂ The hypo- and hyper-eutectic Fe-Si-B glasses were found to crystallize differently. The crystallization processes are discussed in some detail.