Powder mixed electrochemical discharge process for micro machining of C103 niobium alloy

This work demonstrates the viability of the powder-mixed micro-electrochemical discharge machining(PMECDM) process to fabricate micro-holes on C103 niobium-based alloy for high temperature applications.Three processes are involved simultaneously i.e.spark erosion,chemical etching,and abrasive grinding for removal of material while the classical electrochemical discharge machining process involves double actions i.e.spark erosion,and chemical etching.The powder-mixed electrolyte process resulted in rapid material removal along with a better surface finish as compared to the classical microelectrochemical discharge machining(MECDM).Further,the results are optimized through a multiobjective optimization approach and study of the surface topography of the hole wall surface obtained at optimized parameters.In the selected range of experimental parameters,PMECDM shows a higher material removal rate(MRR) and lower surface roughness(R_(a))(MRR:2.8 mg/min and R_(a) of 0.61 μm) as compared to the MECDM process(MRR:2.01 mg/min and corresponding Raof 1.11 μm).A detailed analysis of the results is presented in this paper.

Niobium alloying effect in high carbon equivalent grey cast iron

The effect of niobium on the formation of NbC phase and solidification structure in high carbon equivalent grey cast iron was investigated.The experimental results indicated that an increase in the niobium content is favorable to refining the graphite and eutectic cell;and the pearlite lamellar spacing is reduced.Based on the thermodynamic calculation the formation of NbC is prior to the eutectic reaction.The reduction in the pearlite lamellar spacing is mainly attributed to the decrease of eutectic temperature with the addition of niobium.Additionally,properties including hardness and wear resistance were improved after the addition of niobium.

Diffusion bonding behaviour of β-γTiAl alloys containing high niobium with Ti interlayer by spark plasma sintering

High niobium β-γ TiAl alloy(HNBG) was diffusion bonded using spark plasma sintering with pure Ti as interlayer. The joint microstructural evolution, growth kinetics and mechanical properties were investigated. The joint included three diffusion zones. The β/B2 phase formed in the Zone Ⅰ, α_(2)phase in the Zone Ⅱ, and β-Ti and α-Ti phases in the Zone Ⅲ. The thickness of β/B2 phase, the average grain size of α_(2)phase and the amount of β-Ti phase increased with the increase of bonding temperature or bonding time. The growth activation energies of β/B2 and α_(2)phases were 582 and 253 kJ/mol, respectively. The joint acquired at 1000 °C, 10 min and 10 MPa showed the maximum shear strength of 308 MPa. Fracture mainly occurred along the interfaces between Zone Ⅰ and HNBG alloy, and between Zone I and Zone Ⅱ. Fracture mechanism of the joint was characterized by brittleness rupture along the phase boundary.

Near-net shape processing of spherical high Nb-TiAl alloy powder by gelcasting

Spherical Ti-45A1-8.5Nb-（W,B,Y） alloy powder prepared by an argon plasma process was near-net shape by gelcasting. In the non-aqueous system, methaerylate-2-hydroxy ethyl, toluene, benzoyl peroxide, and N,N-dimethylaniline were used as the monomer, solvent, initiator, and catalyst, respectively. To improve sintering and forming behaviors, many additives were included in the suspension. The concentrated suspension with a solid loading of 70vo1% was prepared. The high Nb-TiA1 powder was analyzed by electron microscopy and X-ray diffraction. It was found that the green bodies had a smooth surface and homogeneous microstructure, exhibiting a bending strength as high as 50 MPa. After sintering at 1480℃ for 2 h in vacuum, uniform complex-shaped high Nb-TiA1 parts were successfully produced.

NEWLY-DEVELOPED AND CHEAP NANOCRYSTALLINE Fe-Cu-Nb-Mo-Si-B ALLOYS FOR SWITCHING MODE POWER SUPPLY

The synthetical soft magnetic properties were reported for newly-developed nanocrystalline Fe73.5Cu1Nb0.9 Mo2.1Si13.5B9 and Fe73.5Cu1Nb0.5 Mo2.5Si13.5B9 alloys. The levels of high-frequency losses of the new alloys are P3/100k=612 and 670 kWm-3, P2/200k=880 and 973kWm-3, P2/500k=4300 and 4600 kWm-3, P0.5/1000k=860 and 920 kWm-3, respectively. They are significantly lower than those of the superior power Mn-Zn ferrite H7c4. The dependence of core loss on frequency and amplitude flux density has been analyzed. The practical applications of the new alloys to switching mode power supplies with the output power of 1 and 2kW were reported.

TEMPERATURE DEPENDENCE OF EFFECTIVE MAGNETIC ANISOTROPY OF Fe-Nb-B ALLOY

The correlation between the effective magnetic anisotropy 〈κ〉 and the temperature T, 〈κ〉-T curve, for the Fe83Nb6B11 alloys as-cast and annealed at 460-580°C was investigated. The experimental results of the 〈κ〉-T curves for nanocrystalline samples were explained using the theory of exchange interaction between α-Fe grains.

High-Temperature Sulfidation of Mo-Nb Alloys

The sulfidation rates and sulfide scales of pure Mo, pure Nb, and Mo Nb alloys are studied. By comparing the rates, an alloy with best sulfidation resistance is found. In addition, the sulfidation kinetics of Mo-50 %Nb is studied in detail.

Single track and single layer formation in selective laser melting of niobium solid solution alloy

Selective laser melting（SLM） was employed to fabricate Nb-37 Ti-13 Cr-2 Al-1 Si（at%）alloy, using pre-alloyed powders prepared by plasma rotating electrode processing（PREP）. A series of single tracks and single layers under different processing parameters was manufactured to evaluate the processing feasibility by SLM, including laser power, scanning speed, and hatch distance.Results showed that continuous single tracks could be fabricated using proper laser powers and scanning velocities. Both the width of a single track and its penetration depth into a substrate increased with an increase of the linear laser beam energy density（LED）, i.e., an increase of the laser power and a decrease of the scanning speed. Nb, Ti, Si, Cr, and Al elements distributed heterogeneously over the melt pool in the form of swirl-like patterns. An excess of the hatch distance was not able to interconnect neighboring tracks. Under improper processing parameters, a balling phenomenon occurred, but could be eliminated with an increased LED. This work testified the SLMprocessing feasibility of Nb-based alloy and promoted the application of SLM to the manufacture of niobium-based alloys.

Effect of stearic acid on the morphological and structural evolution of mechanically milled Nb-based powder

Nb-based powder was fabricated via mechanical grinding. The influence of stearic acid on the grinding process was studied. The slructural evolution and morphological evolution of the milled powder were characterized by X-ray diffraction （XRD）, scanning electron mi- croscopy （SEM）, and energy dispersive spectroscopy （EDS） analysis. It is indicated that an appropriate amount of stearic acid accelerates the particle refinement process and favors the production of superfine Nb-based particles with good dispersivity and high activity. However, an inappropriate amount of stearic acid has an adverse effect on the refinement process.

Decomposition of Nb_(3)Si and mechanical-property improvement by adding appropriate amount of MgO in Nb-16Si-20Ti alloy

Five Nb-16Si-20Ti-xMgO alloys(x=0,0.1,0.5,1.0 and 3.0)were prepared via arc melting in this study,and the effect of MgO addition on their phase composition,microstructure evolution,and mechanical properties was examined.The results demonstrated that MgO reacted with the Nb-Si-Ti alloy while Mg atoms replaced Nb atoms in the Nbss phase.The hypoeutectic alloy was transformed into a hypereutectic alloy upon the addition of 3.0 at%MgO,and the Nb_(3)Si phases decomposed into a fine Nbss/α-Nb5Si3 eutectic structure.The highest fracture toughness was achieved for the Nb-16Si-20Ti-3MgO alloy,with an ambient fracture toughness value of 9.4 MPa·m^(-1/2)due to its largest Nbss phase content and optimal Nbss/α-Nb_(5)Si_(3)eutectic structure.Furthermore,the alloy compressive strength increased with MgO addition.The compressive strength of the Nb-16Si-20Ti-3MgO alloy was 2624.1 MPa,26.0%higher than that of Nb-16Si-20Ti,due to the formation of a solid solution of Mg atoms in the Nbss phase and reinforcement of a small amount of the Ti_(2)O phase.Finally,an increase in the content of the Nbss/α-Nb_(5)Si_(3)eutectic structure increased both the alloy strength and fracture strain.