Oxyacetylene Torch Environment Research Articles

Elevated temperature ablation mechanism and microstructural evolution of W-3Re-xHfC alloys in an oxy-acetylene torch environment

Nozzle materials always withstand ultra-high temperatures (above 2000 °C) in space propulsion and other fields, which results in complex physical-chemical phenomena under actual operating conditions. The ablation mechanism and microstructural evolution of W-3Re-xHfC alloys were investigated to simulate the actual service conditions. Results show an outstanding ablation resistance. The linear ablation rate of the W3Re matrix is 6.67 μm/s, the W-3Re-0.5HfC, W-3Re-5HfC and W-3Re-10HfC alloys are 2.93 μm/s, 2.23 μm/s and 2.26 μm/s, respectively. The linear ablation rates of W-3Re-0.5HfC, W-3Re-5HfC, and W-3Re-10HfC alloys decreased by 66%, 67%, and 67% compared with the W3Re matrix, respectively. Thermochemical oxidation of the W3Re matrix and HfC was the primary ablation mechanism of W-3Re-xHfC alloys. This work contributes to the design and improving the ablation resistance of WRe alloy applications in extreme environments.

Ablation behavior and mechanisms of ZrC-SiC-MoSi2 coated C/C-SiC-ZrC ceramic matrix composites under oxyacetylene torch

To further improve the anti-ablation property of C/C composites in different ablation environments, ZrC−SiC−MoSi2 coatings containing 34 wt.% and 60 wt.% Zr were prepared on C/C−SiC−ZrC ceramic matrix composites via slurry painting (SP) method. And the ablation behavior of the coated composites was investigated in oxyacetylene torch environment with three kinds of fluxes of oxygen and acetylene. The results show that with the increase of Zr content, the particle sizes of ZrC and SiC in the coatings are significantly reduced, with the particles distributing more homogeneously. The linear ablation rates of the coatings with 60 wt.% Zr increase with the increase of oxygen and acetylene fluxes, while for the coatings with 34 wt.% Zr, the linear ablation rates increase at the beginning and then decrease. The ablation mechanisms of the coatings under different conditions were discussed as well. With the increase of oxygen and acetylene fluxes, main ablation mechanisms change from oxidation to oxidation plus evaporation and then to the combination of oxidation, evaporation and denudation.

Enhanced ablation resistance of HfB2-HfC/SiBCN ceramics under an oxyacetylene torch environment

To further improve the ablation resistance of SiBCN ceramics, nanosized HfB2 was introduced by mechanical alloying and subsequent reactive hot-pressing techniques to fabricate HfB2-HfC/SiBCN multiphase ceramics. The mass and linear ablation rates of the 30 vol% HfB2-HfC containing SiBCN ceramics under an oxyacetylene flame for 10 s were lower than those of ZrB2-ZrN/SiBCN and SiBCN, reaching to 0.0025 mg/s and 0.0004 mm/s respectively. Even ablated for 60 s, no trace of cracks appeared on the ablation surface. Oxidation of ceramic matrix, denudation of oxides, erosion by the combustion flow and the re-oxidation of the exposed matrix governed the ablation process.

A Multilayer SiC/ZrB2/SiC Ablation Resistance Coating for Carbon/Carbon Composites

To improve the ablation resistance of carbon/carbon (C/C) composites, a new SiC/ZrB2/SiC multilayer coating is designed and fabricated by a three‐step method of pack cementation, supersonic plasma spraying, and low pressure chemical vapor deposition. In this study, ablation behavior of SiC/ZrB2/SiC coating is investigated under oxyacetylene torch environment. Oxyacetylene ablation testing results show that the linear ablation rate and mass ablation rate of SiC/ZrB2/SiC coated C/C composites are only −5.0 × 10−4 mm s−1 and −9.6 × 10−4 g s−1, respectively, for 20 s ablation under heat flux of 2400 kW m−2. However, the ablative linear rate of ZrB2/SiC coated C/C composites is 7.5 × 10−4 mm s−1 and the ablative mass rate is zero. The better ablation resistance is mainly attributed to a molten SiO2–ZrO2 hybrid glassy layer formed after ablation on the surface of the composites and acting as thermal barrier layer inhibiting inward diffusion of oxygen.

Ablation properties of HfB2 coatings prepared by supersonic atmospheric plasma spraying for SiC-coated carbon/carbon composites

In order to improve the ablation resistance of carbon/carbon (C/C) composites, hafnium boride (HfB2) coatings were prepared on the surface of SiC-coated C/C composites by supersonic atmospheric plasma spraying (SAPS). The anti-ablation property was investigated in an oxyacetylene torch environment under different heat flux. The phase composition, surface and cross-section microstructure and ablation behavior of the prepared coated C/C composites were characterized by using X-ray diffraction and scanning electron microscopy equipped with energy dispersion spectroscopy. The HfB2 coating exhibited excellent ablation resistance under 2400 kW/m2 after ablation for 30 s and no obvious penetrated crack and critical defect could be observed in the coating. The increase of ablation rates with the formation of rugged surface structure and pores indicated that HfB2 coating suffered more serious mechanical denudation and thermochemical erosion. The formation of protective glassy Hf-O layer with low oxygen permeability, generated due to the oxidation of HfB2 phase, inhibited the inward diffusion of oxygen and improved remarkably the ablation resistance of C/C composites.

Preparation and Ablation Performance of Lightweight Phenolic Composite Material under Oxyacetylene Torch Environment

The present study investigates the influence of fiber content on thermal properties of short silica fiber (SSF) reinforced modified resole resin (MRR) composites. For this purpose, different SSF loading composites were prepared: 40, 55, and 65 wt.%. The ablation resistance related to mass loss parameters was quantified by testing under an oxyacetylene flame up to 2300 °C for 30 s. The thermal conductivity of the composite was studied via experimental steady state technique. Thermal stability of the composite material was estimated by means of thermo-gravimetric analysis (TGA), both in air and nitrogen atmosphere. The ablated composite material was characterized by different techniques (XRD, FTIR, and SEM). The results showed that the backface surface temperature of SSF/MRR composites follows the typical variation curve, and linear ablation rate, mass ablation rate, and char yield decrease with increasing silica fiber content. This confirms that 55 and 65 wt.% SSF loading exhibited the best anti-ablation performance and the lowest percentage of char yield. XRD and FTIR analysis of the ablated specimen zone showed the absence of new phase. The thermo-gravimetric analysis confirmed the thermal resistance of SSF/MRR composites in comparison with MRR matrix and the decrease of char with increasing SSF loading. The thermal conductivity of these composites was significantly enhanced by the SSF into the modified resole matrix. This thermal conductivity follows both the rule of mixture and Maxwell models. The overall thermal characteristics of the SSF/MRR composites meet most of the necessary high temperature application criteria.

Microstructure and Ablation Behavior of W Coating Prepared by Atmospheric Plasma Spraying for Zr/Cu Infiltrated C/C Composites

To improve the ablation resistance of carbon/carbon (C/C) composites, W coating prepared by atmospheric plasma spraying (APS) for Zr/Cu infiltrated C/C composites are fabricated, the Zr/Cu infiltrated C/C composites are prepared by reactive melt infiltration (RMI). The microstructural features of the composites are examined by scanning electron microscopy coupled with energy dispersive spectrometry (SEM‐EDS), X‐ray diffraction (XRD), and transmission electron microscopy (TEM). The ablation resistance of the W coated Zr/Cu infiltrated composites are tested in the oxyacetylene torch environment at heat flux of 4186 kW m−2 for 150 s. The results show that the diameter of ablation center and line ablation rate (LAR) of W coated composites are about 3.92 mm and 5.16 × 10−3 mm s−1. Compared to pure C/C and the Zr/Cu infiltrated composites, the diameters of ablation center of W coated composites are reduced by 18.00% and 15.52%, the LAR of W coated composites decreases by 74.52% and 23.55%. Overall, the W coated composites depict good ablation property due to the high melting point of W coating, which can be resistant to high‐temperature oxidation and ablation, the sublimation of WO3 carries away the heat.

Microstructure and ablation performance of SiC–ZrC coated C/C composites prepared by reactive melt infiltration

To improve the ablation resistance of carbon/carbon (C/C) composites, SiC–ZrC coating was prepared by reactive melt infiltration (RMI) on C/C composites. The microstructure and morphology of the coating were characterized by scanning electron microscopy coupled with energy dispersive spectrometry (SEM–EDS), X-ray diffraction (XRD), electron probe microanalysis (EPMA) and transmission electron microscope (TEM). The TEM specimen was fabricated by focused ions beam (FIB). The results show that the SiC–ZrC coating prepared on the condition of optimum parameter exhibits outstanding anti-ablation performance. After ablation for 60 s in oxyacetylene torch environment at heat flux of 4186 kW/m2, the mass ablation rate (MAR) and linear ablation rate (LAR) of the coated composites were 1.18 × 10−3g/s and 2.47 × 10−3 mm/s, which were 83.6% and 54.5% reduction compared with uncoated composites. During the ablation, the formed molten eutectics SiO2–ZrO2 can fill the pores and act as a diffusion barrier for oxygen and heat.

Ablation Mechanism of HfC-HfO2 Protective Coating for SiC-Coated C/C Composites in an Oxyacetylene Torch Environment

To prevent the C/C composites from ablation, HfC-HfO2 protective coating was prepared by supersonic atmospheric plasma spraying. The morphology and microstructure of HfC-HfO2 coating were characterized by X-ray diffraction and scanning electron microscopy. The ablation resistance test was carried out by an oxyacetylene torch. The results show that the as-prepared coating is dense with little pinholes and crack free. The elements Hf, C and O were uniformly distributed in the cross-section. After ablation for different time, the mass ablation rate fluctuated along with the change of ablation time. The ablation process of the surface coating could be divided into rapid oxidation and solid state sintering stages. During ablation, an HfCxOy-HfO2 transitional layer was generated in the coating, which resulted from the active oxidation of HfC. After cooling, some microcracks were observed on the surface of coating, and the structure of cross-section was broken, which were due to the phase transition of HfO2.

Densification and ablation behavior of ZrB2 ceramic with SiC and/or Fe additives fabricated at 1600 and 1800 °C

The effects of Fe and SiC additions on the densification, microstructure, and ablation properties of ZrB2-based ceramics were investigated in this study. The sample powders were conventionally mixed by cemented carbide ball then sintered by spark plasma sintering. The ablation rates and behavior of the ceramics were investigated under an oxyacetylene torch environment at about 3000°C. A sample with high relative density (96.3%), high flexural strength (415.6MPa), and low linear ablation rate (−0.4µm/s) was obtained via SPS at 1600°C. Adding 4vol% Fe was more beneficial to the density of ZrB2 sintered at 1600°C as compared to ZrB2 sintered at 1800°C. The ablation behavior and rates were similar among samples sintered at 1600°C and 1800°C.

SiC/ZrB2–SiC–ZrC multilayer coating for carbon/carbon composites against ablation

Abstract To improve the ablation resistance of carbon/carbon (C/C) composites at high temperature, a ZrB2–SiC–ZrC coating was prepared on the surface of SiC-coated C/C composites by supersonic atmosphere plasma spray (SAPS). Ablation resistance of the coated C/C composites was tested in an oxyacetylene torch environment with a heat flux of 2400 kW/m2 for 120, 150 and 200 s, respectively. After ablation for 120 s, the coating exhibited a three-layered structure consisting of a porous ZrO2 layer, a ZrO2–SiO2 thin layer and a SiC-depleted layer, whereas it transformed into a two-layered structure (ZrO2 recrystallized layer and ZrO2–SiO2 layer) after ablation for 150 s. With the increase of ablation time, the SiC inner coating was almost consumed and a gap emerged between the ZrO2 layer and the C/C matrix after ablation for 200 s. The good ablation resistance of the sprayed coating is mainly attributed to the layered structure acting as a thermal barrier and inhibiting inward diffusion of oxygen.

Mechanical and ablation properties of laminated ZrB2–SiC/BN ceramics

Fully dense laminated ZrB2–SiC/BN ceramics were successfully prepared by tape casting and hot pressing, and the mechanical and ablation properties were investigated in detail. Compared with monolithic ZrB2–SiC ceramics, the flexural strength of laminated ZrB2–SiC/BN ceramics slightly decreased due to the introduction of the weak BN interlayer. However, the fracture toughness of laminated ZrB2–SiC/BN ceramics was significantly improved. The remarkable improvement of fracture toughness was mainly attributed to crack deflection and crack bifurcation. Under oxyacetylene torch environment, the laminated ZrB2–SiC/BN ceramics exhibited an excellent configurational stability compared with monolithic ZrB2–SiC ceramics due to the introduction of weak interlayer.

Effect of pre-oxidation on the ablation resistance of ZrB2–SiC coating for SiC-coated carbon/carbon composites

To improve ablation resistance of carbon/carbon (C/C) composites at high temperature, ZrB2–SiC coating was prepared on surface of SiC-coated C/C composites by supersonic atmosphere plasma spray. The coated C/C composites were pre-oxidized in air at 1373K. In the present work, the influence of pre-oxidation treatment on the microstructure and ablation resistance of ZrB2–SiC coating was investigated. Ablation resistance of coated C/C composites was tested in oxyacetylene torch environment with the heat flux of 2400kW/m2. Results show that the liquid glass phase seals defects in the as-sprayed coating after pre-oxidation for 15min and a dense coating is obtained. The pre-oxidation coating can protect C/C composites for 90s, which is due to the formation of a dense oxides layer and the molten ZrO2 layer.

Ablation behavior of CVD-ZrC coating under oxyacetylene torch environment with different heat fluxes

An ablation resistance ZrC coating composed of micrometer particles was prepared on carbon/carbon composites by chemical vapor deposition. The structure evolution, ablation property and behavior of the coating were investigated under an oxyacetylene torch environment with different heat fluxes. Results show that the ablation performance decreases with the increase of heat fluxes from 2380 to 4180kW/m2. Oxidation erosion is proposed as the major ablation mechanism. The ablated coating consists of three layers (outer ZrO2 layer, transitional ZrCxOy layer and residual ZrC layer). An oxidation progress that the ZrC is oxidized into ZrCxOy firstly and then into ZrO2 is inferred and accelerated by the continuous diffusion of oxygen resulted from the increase of heat fluxes. During different heat flux environments, the coating exhibits efficacious mechanical denudation resistance and the formed transitional ZrCxOy and outer ZrO2 layers act as a good oxygen diffusion barrier, which could be the reason for its high ablation resistance at the temperature of 2000–3000°C.

Structure evolution and ablation behavior of ZrC coating on C/C composites under single and cyclic oxyacetylene torch environment

ZrC ablation resistance coating was prepared on carbon/carbon composites by low pressure chemical vapor deposition using the ZrCl4–C3H6–H2–Ar system. The structure evolution and ablation behavior of the coating under single and cyclic ablation were investigated in an oxyacetylene torch environment. Single ablation results show that the ablated coating consists of three layers (outer ZrO2 layer, transitional ZrCxOy layer and residual ZrC layer). An oxidation progress is inferred that ZrC is oxidized into ZrCxOy firstly and then into ZrO2 in the case of the continuous diffusion of oxygen. Cyclic ablation results show that the effect of crack growth inhibition and the oxygen diffusion limitation of ZrO2 and ZrCxOy layers dominate the ablation of the coating and result in two different ablation behaviors. Based on the role of the ZrO2 and ZrCxOy layers in the single and cyclic ablation, two different ablation modes of the coating are proposed.

Comparison of ablative behaviour for ZrC and ZrC–Cu doped carbon/carbon composites in oxyacetylene torch environment

Carbon/carbon (C/C) composites were doped by Zr and Zr2Cu respectively. The microstructures and ablation properties of two kinds of doped C/C composites were compared. The results indicate that the sweat cooling effect of Cu phase can improve the antiablation properties of the C/C–ZrC composites when Zr2Cu was used as the infiltrator.

Ablation mechanism and properties of in-situ SiAlON reinforced BN–SiO2 ceramic composite under an oxyacetylene torch environment

Ablation mechanism and properties of in-situ SiAlON reinforced BN–SiO2 ceramic composites have been carefully studied under different ablation time. Results showed that the ablation properties depend on the ablation time. When the ablation time increases from 10s to 60s, the mass ablation rate increases from 0.20mg/s to 6.24mg/s and the linear ablation rate increases from 9.0μm/s to 28.1μm/s. The phases of ablation products mainly consist of amorphous SiO2, Mullite, Corundum and B2O. Four time-dependent ablation behaviors contributed to the various ablation regions: oxidation of matrix which includes BN and Si2Al3O7N; evaporation of B2O3(l) and softening of SiO2(s); scouring away of SiO2(l) and Al2O3(l) by high-speed gas stream; evaporation of SiO2(l) and Al2O3(l).

Ablation mechanism and properties of SiCf/SiBCN ceramic composites under an oxyacetylene torch environment

Ablation mechanism and properties of SiCf/SiBCN ceramic composites under an oxyacetylene torch ablation environment were investigated. Ablation products mainly consist of amorphous SiO2 glass and cristobalite. Four time-dependent ablation actions contribute to the various ablation regions: oxidations of SiC fibers and SiBCN matrix, erosion of SiC fibers in the center region, evaporation of SiO(g) and B2O3(g), and high-viscosity SiO2 liquid flowing with ablation gas-stream. Meanwhile, the mass ablation rate and linear ablation rate of SiCf/SiBCN are notably lower than those of Cf/SiBCN.

Effect of zirconia on ablation mechanism of asbestos fiber/phenolic composites in oxyacetylene torch environment

Abstract Micron-size zirconium oxide (ZrO2) was used to improve the thermal stability and ablation properties of asbestos fiber/phenolic composites and to reduce their final cost. ZrO2/asbestos/phenolic composites were prepared in an autoclave by the curing cycle process. The densities of the composites were in the range of 1.64–1.82 g/cm3. The ablation properties of composites were determined by oxyacetylene torch environment and burn-through time, erosion rates and back surface temperature in the first required 20 s. To understand the ablation mechanism, the morphology and phase composition of the composites were studied by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Thermal stability of the produced materials was estimated by means of thermal gravimetric analysis, in air which consisted of dynamic scans at a heating rate of 10 °C/min from 30 to 1000 °C with bulk samples of about 23±2 mg. The thermal stability of the composites was enhanced by adding ZrO2. The results showed that the linear and mass ablation rates of the composites after adding 14 wt% ZrO2 decreased by 58% and 92%, respectively. The back surface temperature of a sample with 14% zirconia was 49% lower than that of pure composite. The SEM studies showed that, modified composites displayed much lower porosity than that of non-modified composite and the destruction of asbestos fibers was very low. On the other hand, it appeared that a thin melted layer of ZrO2 covered the surfaces of zirconia-containing composites.

Microstructures and Properties of the C/Zr-O-Si-C Composites Fabricated by Polymer Infiltration and Pyrolysis

A way to improve the ablation properties of the C/SiC composites in an oxyacetylene torch environment was investigated by the precursor infiltration and pyrolysis route using three organic precursors (zirconium butoxide, polycarbosilane, and divinylbenzene). The ceramic matrix derived from the precursors at 1200 °C was mainly a mixture of SiC, ZrO2, and C. After annealing at 1600 °C for 1 h, ZrO2 partly transformed to ZrC because of the carbothermic reductions and completely transformed to ZrC at 1800 °C in 1 h. The mechanical properties of the composites decreased with increasing temperature, while the ablation resistance increased due to the increasing content of ZrC. Compared with C/SiC composites, the ablation resistance of the C/Zr-O-Si-C composites overwhelms because of the oxide films which formed on the ablation surfaces. And, the films were composed of two layers: the porous surface layer (the mixture of ZrO2 and SiO2) and the dense underlayer (SiO2).