Al2O3 Fibers Research Articles

Diffusion of Ni into Al 2O 3-fibres during hot pressing of [formula omitted] long fibre composites

Intermetallic matrix composite specimens of Ni 3Al-matrix reinforced with continuous Al 2O 3 fibres (FP-fibres) were investigated by means of TEM, SEM, EDS and EPMA with regard to chemical stability during diffusion bonding. The specimens were hot pressed at 1280°C and 20 MPa for 2 h in vacuum and air. The experimental results revealed a noticeable diffusion of Ni into the fibres during hot pressing. The diffusion coefficients of Ni in the fibres were estimated from the analytical results of EPMA-analysis. The estimated values for T = 1280°C were D v Ni = (5 ± 2) × 10 −14cm 2·s −1 for volume diffusion and D gb Ni = (6 ± 2) × 10 −9cm 2·s −1 for grain boundary diffusion. Based on these results it is proposed that Ni-diffusion in the fibres involves both volume and grain boundary diffusion. In addition, oxygen diffusion in the fibres during hot pressing in air is conceived to proceed by diffusion along grain boundaries as well as through the bulk. The influence of Ni- and oxygen-diffusion in the fibres on the formation and growth of Ni-reaction products during hot pressing in air is discussed.

Fabrication of Al2O3-reinforced Ni3Al composites by a novel in situ route

A novel in situ technique has been used to fabricate an Al2O3-reinforced Ni3Al matrix composite. The composite was prepared by first incorporating a low volume fraction of continuous Al2O3 fibers in a Ni3Al alloy containing 0.34 at. pct Zr. Pressure casting was used to embed the fibers. Casting resulted in partial reduction of the Al2O3 fiber by the Zr present in the matrix and the formation of a layer of ZrO2 on the surface of the fibers. The final composite was then prepared by air annealing the precursor composite at 1100 °C for 10 days. Air annealing led to the formation of networks of Al2O3 around the fibers. The matrix in the immediate vicinity of the networks consisted of Ni3Al particles in a matrix of disordered α-Ni(Al). The Al2O3 networks raised the yield and tensile strength of the material by 35 and 18 pct, respectively. The composite had a tensile ductility of 14 pct.

Erosion resistance of thermal insulating materials in streams of ionized gases

A study is summed up that was concerned with the erosion resistance in a stream of ionized gases of a composite made up of a corundum matrix and polycrystalline Al2O3 fibers in comparison with a ceramic composite using an oxygen-free compound. A process was developed for the manufacture of odd-shaped products of high erosion resistance.

Preparation and mechanical properties of high-purity Al2O3 fibre/Al2O3 matrix composite

Al2O3 matrix composites with unidirectionally oriented high-purity Al2O3 fibre with and without carbon coating, were fabricated by the filament-winding method, followed by hot-pressing at 1573–1773 K. The composite with non-coated Al2O3 fibre exhibited a bending strength (594 MPa) comparable to that of monolithic Al2O3 (589 MPa). While the composite with a carbon-coated fibre had lower strength (477 MPa), it showed improved fracture toughness (6.5 MPa m1/2) compared to the composite with an uncoated fibre (4.5 MPa m1/2) and monolithic Al2O3 (5.5 MPa m1/2). This toughness enhancement was explained based on the increased crack extension resistance caused by the fibre pull-out observed by SEM at the notch tip.

Compressive and tribological properties of Al2O3 fibre and hexagonal BN particle hybrid reinforced Al-Si alloys

Al2O3 fibre-hexagonal BN particle hybrid reinforced aluminium-silicon alloys were fabricated by centrifugal force infiltration route. Hardness test and ultimate compressive test results are reported. The wear and friction properties of hybrid MMCs was investigated by means of a block-on-ring (bearing steel) type wear rig in a dry sliding condition. It is shown that the hardness and ultimate compressive strength of hybrid MMCs was evidently decreased with the addition of hexagonal BN particles, however, the wear rate and coefficient of friction of hybrid MMCs was improved simultaneously with increase of BN particle volume fraction, especially for the higher applied loads in the test.

Scanning Force Microscopy Study of Ceramic Fibers for Advanced Composites

The surface roughness and topography of three different Al2O3 fibers were evaluated using atomic force microscopy (AFM). The fibers used were as‐received, refractory‐metal coated, and Y2O3/refractory‐metal duplex‐layer coated. The refractory‐metal coating and Y2O3 coating on the Al2O3 fibers increased the average surface roughness from 13.3 to 17.1 and 18.8 nm, respectively. The topographic image of the fibers evaluated by AFM was compared to that obtained by scanning electron microscopy. Lateral force microscopy (LFM) was used to measure the distribution of the friction force on the refractory‐metal‐coated Al2O3 surfaces, with friction coefficients ranging from 0.2 to 0.8; the average friction coefficient was 0.38. Tailoring the mechanical properties at fiber/matrix interfaces by surface modification of Al2O3 fibers to improve the overall mechanical properties of the composites also was proposed.

Interfacial chemical stability during diffusion bonding of Al 2O 3-fibres with Ni 3Al- and NiAl-matrices

Intermetallic matrix composites of Ni 3Al- and NiAl-matrix reinforced with continuous Al 2O 3 fibres were investigated by means of TEM, EDS and HRTEM with regard to interfacial reactions during diffusion bonding. The specimens were fabricated by hot pressing both in vacuum (2 × 10 −4 Pa) and in air for 2–8 h at 1200–1280°C for the Ni 3Al-matrix and at 1300–1450°C for the NiAl-matrix, respectively. Experimental results revealed a diffusion of Ni from the Ni 3Al-matrix into the fibres during diffusion bonding. As a consequence of the diffusion process a chemical reaction took place in the specimens with Ni 3Al-matrix hot pressed in air: particle-shaped reaction products (Ni-spinel) were observed in the fibres. In addition, thin films of about 5–20 mm thickness appeared in some sections of the interface in specimens with Ni 3Al-matrix hot pressed in vacuum. In the film the lattice planes were disordered and porous. In other sections (Mg,Ni)-spinels (Mg,Ni)Al 2O 4 were formed as interfacial reaction products, when MgO as impurity had segregated to the surface of the fibres prior to diffusion bonding. In contrast to the results on Ni 3Al, specimens with NiAl-matrix showed excellent chemical stability during hot pressing both in vacuum and in air: only minor diffusion of Ni into the fibres and no reaction products could be detected. The potential influence of interfacial behaviour on the mechanical properties of the composites will be discussed.

Origin of θ′ Relaxation in Reinforced and Unreinforced AlCu Alloys

When AlCu alloys are in the θ′ precipitation state, they exhibit a peak (P2) in their internal friction spectrum as a function of the temperature. In this connection, an unreinforced Al-4% Cu alloy and some Al-4% Cu based metal matrix composites (MMC) reinforced with 10%, 20%, and 30% Al2O3 fibers were characterized by internal friction measurements (IF or Q−1). The microstructure of the AlCu based composites has been found particularly favorable for the appearance of the P2 peak, and enhances θ′ relaxation. This kind of result has led us to a new interpretation of θ′ relaxation in AlCu alloys. θ′ relaxation is important in AlCu based composites because the expected industrial utilization temperature of these materials is around 250 °C, and this implies a θ′ precipitation state for their working conditions.

Processing and Characterization of Fiber Reinforced Intermetallic Matrix Composites

Abstract A series of intermetallic matrix composites reinforced with Al2O3 based fibers were fabricated by pressure casting. The Al2O3 based fibers used were DuPont's 20 μm diameter Fiber FP and PRD-166 fiber, Mitsui's 10 μm diameter Almax fiber, and Saphikon's 125 μm diameter single crystal Al2O3 fiber. The intermetallic matrices employed were alloys based on Ni3Al, NiAl, Fe3Al, Ti3Al+TiAl, and Nb2Al+NbAl3. Optical, scanning and transmission electron microscopy were used to investigate the microstructure of the composites and the fibers. Tensile testing was conducted to determine the Weibull mean strength of the fibers in the as-received and heat treated conditions. The effect of fiber gage length on the Weibull mean strength of the PRD-166 and Fiber FP was evaluated. Indentation tests were performed to determine the effect of alloying additions on the fiber/matrix bond strength in shear in Saphikon fiber reinforced Ni3Al composites.

Growth and laser properties of Ti:sapphire singlecrystal fibres

The growth of Ti:sapphire single crystal fibres in various atmospheres and different source rods is investigated by using the laser heated pedestal growth method. A tunable fibre laser with a 56.5 nm tuning range has been demonstrated in a 350 µm diameter 11.2 mm long Ti3+:Al2O3 fibre.

Internal friction in AlCu-Al2O3 metal-matrix composites

In metal-matrix composites (MMCs), the metal matrix is exposed to plastic deformation and damage accumulation in the region close to the reinforcements, following mechanical or thermal stress. In this connection, Al-4 wt pct Cu-based MMCs reinforced with 20 vol pct Al2O3 fibers were characterized by internal friction (IF) measurements. The IF measurements as a function of the vibration amplitude present a solid friction peak connected with the loosening of metal-fiber interfaces, while plastic deformation was associated with a high amplitude IF background. On this basis, IF measurements allowed us to identify the distribution of internal stresses and damage accumulation at matrix-fiber interfaces or plastic flow in the matrix in different thermomechanical conditions. Furthermore, IF measurements allowed damage accumulation consequent to mechanical fatigue to be followed.

Tensile Properties of Alumina Fibers Using Hot‐Grips

Tensile testing of single‐crystal Al2O3 fibers was conducted using a hot‐grip method developing during this study. Fracture strength was measured between 25° and 1500°C and was found to decrease with increasing temperature. However, a strength minimum, observed by others between 400° and 900°C, appeared to be absent The experimental results are in good agreement with calculated fracture strength values based on the fracture toughness of cleavage planes up to 1200°C. Strain rate experiments carried out at 1300°C indicate that strength is strongly time dependent. Fracture originates from both surface flaws and internal pores in the fibers.

Optimisation of alloy–alumina fibre combination for magnesium based metal matrix composites

AbstractResults are reported on the compositional and structural features of metal/ceramic interfacial reactions in a series of magnesium based composites containing Al2O3 fibres (3 μm diameter) produced via liquid metal infiltration of preforms. The composites employed a range of matrix compositions and fibres of different porosities and in some cases binders were used. The practical objective was to optimise the combination of matrix and fibre to reduce the extent to which alumina reacts with liquid magnesium. Detailed electron microscopy has shown that the dominant factor in minimising this reaction is reduction in the extent of interconnecting porosity in the fibres. The presence of alloying elements, such as aluminium in the matrix plays a more limited role in reducing the extent of interface reaction.MST/3021

Fiber strength and fiber/matrix bond strength in single crystal Al2O3 fiber reinforced Ni3Al based composites

A series of single-crystal Al[sub 2]O[sub 3] fiber (Saphikon), reinforced Ni[sub 3]Al-based composites were fabricated by a liquid metal infiltration technique, pressure casting. Tensile testing and indentation techniques have been employed to measure fiber strength and fiber/matrix interfacial debond shear stress. The Weibull mean strength of the fiber has been observed to decrease drastically upon handling, exposure to high temperature, and casting. Alloying of Ni[sub 3]Al with Ti has resulted in a further decrease in fiber strength. Thermal expansion mismatch between the fiber and matrix led to the formation of compressive twins in the fiber. These twins, forming on [l brace][bar 1]102[r brace] planes, produced cracks at their intersections, which were parallel to the fiber axis, c-axis. Twin-induced fiber cracking was observed in all cases, but most predominantly when Cr was present. While addition of Cr at the 1 at. pct level-had no appreciable effect on the interfacial debond shear stress, addition of 0.5 at. pct Cr resulted in an approximately threefold increase in debond stress, from 19 MPa to about 54.5 MPa. Alloying of Ni[sub 3]Al with Cr has also resulted in partial dissolution of the Al[sub 2]O[sub 3] fiber. Addition of Ti had a moderate effect on increasingmore » the fiber/matrix bond strength.« less

Fatigue damage development in Al 2O 3/Al composite

Abstract Fatigue damage development in two aluminium matrix (Al7SiO.6Mg and Al5Si-3Cu1Mg) composites reinforced with discontinuous Al2O3 fibres has been monitored by means of acoustic emission (AE). The AE signals (RMS) recorded during the tests clearly exhibit three distinct stages which correspond to crack initiation, dominant crack formation and stable propagation. Generally speaking, the cracks initiated at a high load level form close together and a dominant crack forms easily. By contrast, at a low load, initiated cracks are widely separated and the formation of a dominant crack is difficult. If there are large defects in the composite, the first stage is absent, even at low load. In the first stage, little change in microstructure and modulus of the composite is observed; in the second, fibre fracture, interface debonding and matrix cracking occur and there are often sinusoidal cracks in the matrix; in the last stage, the principal characteristic is stable propagation of the dominant crack. The degradation of the elastic modulus of the composite in the last two stages is small.

Interfacial stability and mechanical properties of Al2O3 fiber reinforced Ti matrix composites

The mechanical properties of the interfaces in an Al2O3 fiber reinforced β-21S Ti alloy have been evaluated by using fiber pushout tests. The Al2O3 fibers were coated with a refractory metal and Y2O3 which served as a diffusion barrier during the HIPing used to produce the metal matrix composites. By doing fiber pushout tests, the interfacial fracture was found to occur at the interface between the refractory metal and the Y2O3. The interfacial shear strength and interfacial frictional stress were measured to be 323 and 312 ± 2 MPa, respectively. The interfacial frictional stress, which is due to asperity interlocking during the fiber sliding, was correlated to the surface roughness of the coated Al2O3 fiber obtained with the aid of an atomic force microscope. The measured surface roughness of 18.8 ± 2.2 nm was related to the frictional stress through Hutchinson's model.9 The frictional coefficient between the Al2O3 fiber and the Ti matrix is calculated to be 0.32 ± 0.02.

特集 ニューコンポジット材料 Ｎｉ３Ａｌ基複合材料の高温引張特性に及ぼすアルミナ形状の影響

Al2O3 fiber and/or particle reinforced Ni3At matrix composites were produced by elemental powder metallurgy, The high temperature tensile properties of the composites were investigated in the connection with microstructures. The results were summaried as follows;The distribution of short Al2O3 fiber in Ni3Al matrix was more uniform than that of long Al2O3 fiber. The grain growth of matrices in the composites was suppressed by adding A1203 particles. The yield strength of every composites increased with increasing temperature to the peak temperature about 800K and then it degraded abruptly above that temperature. The complex addition of both short fiber and particle was the most effective to improve high temperature tensile properties.

Strength of Single Crystal Al2O3 Fibers in Ni-Based Intermetallic and Superalloy Composites

AbstractStrength degradation of single crystal Al2O3 fibers due to the effect of fiber/matrix interaction and processing of NiAl and superalloy matrix composites, was investigated. Strength loss was quantified by tensile testing fibers that were exposed to the matrix alloy using two different methods. In one method, the fibers were incorporated into a composite by either the Powder Cloth (P-C) or binderless powder technique. The fibers were then extracted from the composite by chemical dissolution of the matrix and subsequently tensile tested and examined by scanning electron microscopy. In the other method, fibers were sputter-coated with a similar matrix composition and heat-treated to simulate conditions similar to those experienced during composite powder fabrication methods. In the sputter coating method, the contribution of fiber-matrix reaction on fiber strength loss was isolated from the effects of the various mechanical loads which are present during powder fabrication. For all matrices studied, significant strength loss was observed both in fibers extracted from composites and in fibers sputter-coated and annealed. Although surface ridges and pores were observed on the degraded fibers, it remains uncertain whether these features were responsible for the strength loss.

Pip Processing, Microstructure and Properties of Si34N Fiber and Al2O3 Fiber Reinforced Silicon Nitride

ABSTRACTPolymer infiltration/pyrolysis (PIP) processing has the potential to become an affordable means of manufacturing continuous fiber-reinforced ceramic-matrix components. The PIP method is very similar to the well-known polymer-matrix and carbon-carbon composite manufacturing techniques, the major difference being the use of a preceramic polymer in place of the organic polymer or carbon precursor. To date, the majority of research in the field of preceramic polymers has centered on precursors to silicon carbide (SiC). The Southwest Research Institute (SwRI) has focused on the development of polymeric precursors to silicon nitride (Si3N4) because its high-temperature strength, resistance to oxidation, and other properties make it an attractive candidate for many advanced high-temperature structural applications. PIP Si3N4 composites with NICALON SiC fiber reinforcement have exhibited good fracture toughness (KIC ∼ 16MPa·m1/ 2). We report here processing, microstructure and preliminary mechanical properties of two new PIP Si3N4 composites. One is reinforced with Tonen Si3N4 fiber (plain weave) while the other is reinforced with ALMAX Al2O3 fiber (8 Harness satin weave).

Hot‐Grip Tensile Method for Alumina‐Fiber Testing

A new tensile test method has been developed for high‐temperature testing of Al2O3 fibers. The advantage of this technique is that it enables testing of ceramic fibers up to 1500°C while the entire sample, including the grips, is within the hot zone. The most critical stage in the entire testing procedure is the alignment of test specimen with respect to the loading axis. The success rate of this testing method is currently around 60%.