Ti Mixed Powder Research Articles

Microstructure and properties of bilayered B4C-based composites prepared by hot-pressing

Bilayered B4C-based composites were prepared by hot-pressing method. One layer was a B4C ceramic layer using C and Ti powders as sintering assistants. The other layer was a B4C ductile layer named as BST layer, in which TiC, Si and Ti mixed powders were added to synthesize Ti3SiC2 phase to improve toughness of B4C. Although XRD results showed that no Ti3SiC2 was found in the BST layer, SEM and EDS analyses proved that trace amount of lamellar Ti3SiC2 structure was observed under high magnification fractographs in the BST layers with additive contents (x) equal to 30 and 40 wt%. Both the flexural strength and fracture toughness of the bilayered B4C-based composite increased with the increase in the amount of additions in the BST layer, reaching optimum values of 550 MPa and 6.6 MPa m1/2 at x = 40 wt%, respectively.

Laser alloying with Fe–B4C–Ti on AA6061 for improved wear resistance

ABSTRACT To improve the wear resistance of AA6061 aluminium alloy, Fe-based composite coatings were prepared by laser surface alloying with Fe–B4C or Fe–B4C–Ti mixed powders. Microstructures, phase compositions and wear properties were investigated. The results indicated that the coating fabricated with Fe–B4C was mainly composed of FeAl, Fe3Al, Fe4Al13, CrB, Cr2B, Cr23C6, Al4C3, (Fe, Cr) and α-Al phases. When adding Ti in the precursor powders, TiB2 and TiC were also well detected. In-situ synthesised TiB2 particles dispersed on the matrix in a hexagonal platelike structure or closely agglomerated and connected with each other to form a whole. The formation mechanism of TiB2 in different morphologies was further discussed. Compared with the 6061 Al substrate, the micro-hardness of the alloyed coatings was improved to 5.7–6.5 times. With the addition of Ti, the wear volume loss reduced to 10% of that of the substrate, indicating a significant improvement in wear resistance.

In-situ TiB2-TiC reinforced Fe-Al composite coating on 6061 aluminum alloy by laser surface modification

To improve the wear resistance of 6061 aluminum alloy, we have reported the fabrication of in-situ TiB2-TiC reinforced Fe-Al composite coatings by laser alloying with Fe-based self-fluxing alloy, B4C and Ti mixed powder. Two Ti contents, which are 30 wt. % and 45 wt. %, in the alloyed coatings were investigated as comparisons, so that investigate phase compositions, microstructures and wear resistance of the alloyed coatings. Additionally, the disregistry between (0001)TiB2 and (111)TiC planes were calculated, of which the formation mechanism of TiB2/TiC composite structure was further analyzed. It was found that the alloyed coatings mainly consisted of TiB2, TiC, Fe4Al13, Cr2B, Cr7C3, Al3Ti and α-Al. With the addition of 30 wt. % Ti, we found that TiC nucleated heterogeneously on the surface of short rod-like TiB2, forming TiB2/TiC composites. The interface was well bonded with a low disregistry of 1.049 %. The average micro-hardness of the composite coating was larger than 7 times of the substrate with a high value of 520 HV0.2. Moreover, a 92.8 % reduction in the volume loss enunciated a significant enhancement in wear resistance. Nevertheless, with the increase of Ti component in the alloyed coating, the supportability of the metal matrix to the reinforcements decreased, resulting in a slight reduction of the micro-hardness and wear resistance.

Reactive composite brazing of C/C composite and GH3044 with Ag–Ti mixed powder filler material

In this study, a novel Ag–Ti reactive composite brazing technology was employed to join carbon fiber reinforced carbon matrix composite (C/C) to Nickel-based superalloy GH3044. The microstructural evolution mechanism and the effects of process parameters on the microstructures and shear strength of the brazed joints were investigated systematically. The results showed that, during the brazing holding stage, Ti (α-Ti) in the liquid phase would convert to β-Ti (above 1020°C) or react with Ag formed AgTi (below 1020°C). Solid phase β-Ti or AgTi inhibited the loss of the molten filler material, thus forming a thicker interlayer, which was beneficial to relieve the residual stress of the joints. After brazing, an Ag matrix composite interlayer reinforced by in situ synthesized phases and a few residual Ti particles could be obtained. Notably, the reinforcing phases were various with different brazing parameters. Under weaker parameters (lower Ti content, lower temperature and shorter holding time), the reinforcing phases were mainly in situ synthesized AgTi phase and residual Ti particles, with which the Ag matrix composite interlayer had good plasticity and low coefficient of thermal expansion. As a result, the residual stress of the joints was further effectively relieved. Under stronger parameters, the reinforcing phases were mainly brittle phases Ti2Ni and Cr1.93Ti1.07, which increased the brittleness of the composite interlayer. The maximum shear strength of the joints reached 45.8 MPa brazed at 1020°C for 30 min using Ag–20Ti (Wt.%).

Characterisation of multiphase ceramic coatings fabricated via laser in situ reaction technology

ABSTRACTCoatings are pre-fabricated on the China low activation martensitic (CLAM) steel via thermal spraying using Cr–Fe–Al–Ti mixed powders. Crystalline and amorphous multiphase ceramic coatings are formed by a new laser surface in situ prefabricated coatings in situ reaction technology under atmospheric environments based on the Standard Gibbs free-energy theory. The grain boundary of incomplete recrystallisation section and perfect crystallisation section can be observed clearly by high-resolution transmission electron microscopy. The Al2O3 and TiO2 are found to be formed in the crystallisation section. In addition, we adopt a new method to measure bonding strength of coating and base material, and the average shear strength is found to be 290 MPa. Further finite-element analysis shows that the shear stress distribution between the coatings and substrate is consistent with the experimental data. The average microhardness of the coatings is found to reach 1864.19 HV0.2.The coatings also exhibit the strongest liquid Pb corrosion resistance. This technique may be important in technological improvement of surfaces of the candidate structural materials for the accelerator-driven sub-critical system, which is usually applied to handle the nuclear waste under extreme conditions.

Simultaneous Synthesis and Sintering of Al2O3/TiN Composites using Capsule-free N2-HIPing from Al2O3 and Fine Ti mixed Powder Compacts

Synthesis of dense composite materials with the compositions of Al2O3/TiN=100/0∼90/10 vol% has been attempted directly from Al2O3/Ti mixed raw powder compacts using capsule-free N2 hot isostatic pressing (HIP). Fine Ti powders (0.3 μm in diameter) with a small amount of TiN0.3 phase were prepared by thermal decomposition of fine TiH2 powders at 400°C for 3.6×103 s in a vacuum, followed by thermal treatment in N2. Then, Al2O3/Ti mixed powder compacts with homogeneously dispersed Ti particles were fabricated and then HIP-sintered. During the first stage of HIPing [1350°C/6 MPa/3.6×103 s], solid/gas reaction between Ti and N2, in which both were contained in the powder compacts, was introduced to form TiN. Then, after the successive second stage of HIPing [1350°C/196 MPa/7.2×103 s], the most of sintered composites consisting of Al2O3 and TiN phases reached to a higher relative density than 98.5 % with closed pores, nevertheless a capsule-free HIPing. Dispersion of TiN particles (0.30∼0.35 μm) just formed suppressed the grain growth of Al2O3 during sintering. Mechanical properties, such as bending strength (σb), Vickers hardness (HV), and fracture toughness (KIC) have been evaluated as a function of TiN content.

Pre-nucleation techniques for enhancing nucleation density and adhesion of low temperature deposited ultra-nanocrystalline diamond

Effect of pre-nucleation techniques on enhancing nucleation density and the adhesion of ultra-nanocrystalline diamond (UNCD) deposited on the Si substrates at low temperature were investigated. Four different pre-nucleation techniques were used for depositing UNCD films: (i) bias-enhanced nucleation (BEN); (ii) pre-carburized and then ultrasonicated with diamond powder solution (PC-U); (iii) ultrasonicated with diamond and Ti mixed powder solution (U-m); (iv) ultrasonicated with diamond powder solution (U). The nucleation density is lowest for UNCD/U-substrate films (∼ 10 8 grains/cm 2), which results in roughest surface and poorest film-to-substrate adhesion. The UNCD/PC-U-substrate films show largest nucleation density (∼ 1 × 10 11 grains/cm 2) and most smooth surface (8.81 nm-rms), whereas the UNCD/BEN-substrate films exhibit the strongest adhesion to the Si substrates (critical loads = ∼ 67 mN). Such a phenomenon can be ascribed to the high kinetic energy of the carbon species, which easily form covalent bonding, Si–C, and bond strongly to both the Si and diamond.

WEAR AND OXIDATION RESISTANCE COATINGS FABRICATED ON Ti-6Al-4V BY LASER SURFACE ALLOYING TECHNIQUE

Composite coatings are produced by laser surface alloying of Ti-6Al-4V with B+Ti and B+Ni+Ti mixed powders. Test results show that the coatings have high hardness, excellent wear and oxidation resistance compared with the as-received sample. In addition, the samples alloyed with B+Ni+Ti have better wear and oxidation resistance than that alloyed with B+Ti .

Preparation of Functionally Graded Materials by Pulse Current Pressure Sintering of Ball Milled Al-50 at%Ti Powder

A functionally graded material (FGM) laminated with five layers composing of Al, Ti and Al 3 Ti phases was prepared from an equimolar mixture of Al and Ti powders by combination of ball milling and pulse current pressure sintering (PCPS) processes. The characteristics of the FGM are as follows. (1) The volume fraction of Al 3 Ti phase in the laminated layers increases with increasing milling period of Al-50 at%Ti mixed powder. This results from the accelerated formation of Al 3 Ti in the PCPS process due to refinement of Al and Ti composite particles during milling. (2) The average value of Vickers hardness for each laminated layer of the FGM increases with increasing content of Al 3 Ti phase in the layer. The average hardness values of the five layers are 28, 165, 258, 425 and 520 HV, respectively.

Effects of Pressure and Temperature on Consolidation of Nanocrystalline MA Powder of Al-10.7 at%Ti-0.6 at%Fe Supersaturated Solid Solution

The powder of a single phase of the Al-10.7 at%Ti-0.6 at%Fe supersaturated solid solution with an average crystallite size of 11 nm has been obtained from a pure Al and Ti mixed powder by means of a high energy planetary ball mill. The mechanically alloyed (MA) powder was consolidated into cylinders 4 mm in diameter and 2.5 mm in height at temperatures of 473773 K under hydrostatic pressures of 0.1 MPa3 GPa. The consolidation at high temperatures causes the decomposition of the supersaturated solid solution obtained by MA, whereas the compacts consolidated at low temperatures retain the supersaturated solid solution and nanostructure. The upper limiting temperature where the compact can retain the supersaturated solid solution becomes higher with increasing consolidation pressure, and the application of high pressure consequently permits consolidating the MA powder at higher temperature without decomposing the supersaturated solid solution. On the other hand, the higher consolidation pressure and temperature can give higher density and hardness to the compact. Thus the application of high pressure is effective for the consolidation of MA powder with the retention of the supersaturation and nanostructure.

高エネルギー遊星ボールミルによるAl-6 at%Ti混合粉末のメカニカルアロイング過程

The mechanical alloying(MA) process of Al-6 at%Ti mixed powders under a surging mode of a high energy planetary ball mill in Ar gas, at the maximum centrifugal acceleration of 40, 80, 120 and 150 G(G is the gravitational acceleration), was investigated by means of microscopic observation, X-ray diffraction, hardness measurement and quantitative analysis of the composition. The MA process proceeds in the following three stages; At the 1st stage both the coalescence of Al and Ti elemental powders and adhering on the pot-wall and the surface of balls occur. The amount of such adhesions increases with milling time. At the 2nd stage, almost all Al-Ti mixed powders adhere on the pot-wall and the ball surfaces, and the dissolution of Ti and Fe atoms into Al powders, work-hardening and the refining of the crystal grains to the nano-size proceed under compressional, frictional and shearing stresses, due to the surging motion of the milling balls. At the 3rd stage, the hardened(Hv: 400∼500) powders, consisting of nano-size crystals of Al-6 at%Ti-1 at%Fe supersaturated solid solution, fall down from the pot-wall and the ball surfaces during milling. In the 3rd stage, the higher the MA energy, the larger the amount of the powders obtained and the greater the hardness of the powders. At the same time, the higher milling intensity caused the faster progress of the MA process. The average grain size of the Al-6 at%Ti-1 at%Fe alloy powders milled for a long time is from 13 to 17 nm, depending on milling intensity during MA. Higher milling intensity tends to bring a smaller grain size. No amorphous phase is detected.

Consolidation of Mechanically Alloyed Al-10.7 at%Ti Powder at Low Temperature and High Pressure of 2 GPa

The powder of a single phase of the Al-10.7 at%Ti supersaturated solid solution with an average grain size of 11 nm has been obtained from a pure Al and Ti mixed powder by means of a high energy planetary ball mill. The mechanically alloyed powder was consolidated into cylinders 4 mm in diameter and 2.5 mm in height at 573 and 623 K under 2 GPa. The compact consolidated at 573 K under 2 GPa retained the supersaturation and nanocrystals and showed a high relative density of about 98% and a high Vickers hardness of about 440.

Effects of the atmosphere on the mechanical alloying process of Al25at.%Ti mixed powder

The mechanical alloying process of Al25at.%Ti mixed powders has been investigated in Ar gas and in air using an attritor type of ball mill. Refinement of mechanically-alloyed powder particles proceeds faster in air than in Ar. However, dissolution of Ti into Al powders proceeds more slowly in air than in Ar because of accelerated oxidation of Al powders in air. The crystal size of mechanically-alloyed composite powders becomes smaller in Ar than in air, but crystal strain becomes larger in air than in Ar.

Al-20 mass%Ti混合粉末のメカニカルアロイング

Alloying processes, formation of amorphous phase and hardening of Al-20 mass% (12.4 at%)Ti mixed powders during mechanical alloying with an Attritor type of ball mill, have been investigated by means of optical, scanning and transmission electron microscopy, X ray analysis and hardness measurements.The mechanical alloying (MA) process detected consists of flake-forming, cold welding of the flaked powders, fracturing of the composite powders, formation of solid solution and amorphous phase. The amount of solute titanium in the composite powder after 493.2 ks MA was estimated to be about 17 mass% from the lattice parameter measurement and grain sizes of the matrix aluminum were in the range from about 20 to 60 nm. The amount of oxygen in mechanically alloyed powders increased with milling time, and dispersions of Al2O3 particles were observed by TEM. The spherorized composite powders with the average particle size of 0.6 μm after 2200 ks MA were amorphous. The amorphous particles showed halo patterns in electron diffraction and showed no grain boundary, no dislocation and few Al2O3 particles in TEM. A remarkable increase in hardness of the composite powders was explained in terms of solid solution hardening of titanium in aluminum, dispersion hardening of Al2O3 particles, work-hardening and hardening by grain refinement.