Ablation behaviour and mechanical performance of ZrB_(2)-ZrC-SiC modified carbon/carbon composites prepared by vacuum infiltration combined with reactive melt infiltration

The development of advanced aircraft relies on high performance thermal-structural materials,and carbon/carbon com-posites(C/C)composited with ultrahigh-temperature ceramics are ideal candidates.However,the traditional routes of compositing are either inefficient and expensive or lead to a non-uniform distribution of ceramics in the matrix.Compared with the traditional C/C-ZrC-SiC composites prepared by the reactive melt infiltration of ZrSi_(2),C/C-ZrB_(2)-ZrC-SiC composites prepared by the vacuum infiltration of ZrB_(2) combined with reactive melt infiltration have the higher content and more uniform distribution of the introduced ceramic phases.The mass and linear ablation rates of the C/C-ZrB_(2)-ZrC-SiC composites were respectively 68.9%and 29.7%lower than those of C/C-ZrC-SiC composites prepared by reactive melt infiltration.The ablation performance was improved because the volatilization of B_(2)O_(3),removes some of the heat,and the more uniformly distributed ZrO_(2),that helps produce a ZrO2-SiO2 continu-ous protective layer,hinders oxygen infiltration and decreases ablation.

Theoretical study of reactive melt infiltration to fabricate Co-Si/C composites

Cobalt-silicon based carbon composites(Co–Si/C)have established a noteworthy consideration in recent years as a replacement for conventional materials in the automotive and aerospace industries.To achieve the composite,a reactive melt infiltration process(RMI)is used,in which a melt impregnates a porous preform by capillary force.This method promises a high-volume fraction of reinforcement and can be steered in such a way to get the good“near-net”shaped components.A mathematical model is developed using reaction-formed Co–Si alloy/C composite as a prototype system for this process.The wetting behavior and contact angle are discussed;surface tension and viscosity are calculated by Wang’s and Egry’s equations,respectively.Pore radii of 5μm and 10μm are set as a reference on highly oriented pyrolytic graphite.The graphs are plotted using the model,to study some aspects of the infiltration dynamics.This highlights the possible connections among the various processes.In this attempt,the Co–Si(62.5 at.%silicon)alloy’s maximum infiltration at 5μm and 10μm radii are found as 0.05668 m at 125 s and 0.22674 m at 250 s,respectively.

Microstructure and Oxidation Behavior of ZrB_(2)-SiC Ceramics Fabricated by Tape Casting and Reactive Melt Infiltration

ZrB_(2)-based ceramics typically necessitate high temperature and pressure for sintering,whereas ZrB_(2)-SiC ceramics can be fabricated at 1500℃using the process of reactive melt infiltration with Si.In comparison to the conventional preparation method,reactive synthesis allows for the more facile production of ultra-high temperature ceramics with fine particle size and homogeneous composition.In this work,ZrSi_(2),B4C,and C were used as raw materials to prepare ZrB_(2)-SiC via combination of tape casting and reactive melt infiltration herein referred to as ZBC ceramics.Control sample of ZrB_(2)-SiC was also prepared using ZrB_(2) and SiC as raw materials through an identical process designated as ZS ceramics.Microscopic analysis of both ceramic groups revealed smaller and more uniformly distributed particles of the ZrB_(2) phase in ZBC ceramics compared to the larger particles in ZS ceramics.Both sets of ceramics underwent cyclic oxidation testing in the air at 1600℃for a cumulative duration of 5 cycles,each cycle lasting 2 h.Analysis of the oxidation behavior showed that both ZBC ceramics and ZS ceramics developed a glassy SiO_(2)-ZrO_(2) oxide layer on their surfaces during the oxidation.This layer severed as a barrier against oxygen.In ZBC ceramics,ZrO_(2) is finely distributed in SiO_(2),whereas in ZS ceramics,larger ZrO_(2) particles coexist with glassy SiO_(2).The surface oxide layer of ZBC ceramics maintains a dense structure because the well-dispersed ZrO_(2) increases the viscosity of glassy SiO_(2),preventing its crystallization during the cooling.Conversely,some SiO_(2) in the oxide layer of ZS ceramics may crystallize and form a eutectic with ZrO_(2),leading to the formation of ZrSiO_(4).This leads to cracking of the oxide layer due to differences in thermal expansion coefficients,weakening its barrier effect.An analysis of the oxidation resistance shows that ZBC ceramics exhibit less increase in oxide layer thickness and mass compared to ZS ceramics,suggesting superior oxidation resistance of ZBC ceramics.

Microstructure and Mechanical Properties of C/C-ZrC-SiC Composites Fabricated by Reactive Melt Infiltration with Zr,Si Mixed Powders

To meet the increasing demand for advanced materials capable of operation over 2000 ℃ for future thermal protection systems application, C/C-ZrC-SiC composites were fabricated by reactive melt infiltration （RMI） with Zr, Si mixed powders as raw materials. The structural evolution and formation mechanism of the C/C- ZrC-SiC composites were discussed, and the mechanical property of the as-prepared material was investigated by compression test. The results showed that after the RMI process, a special structure with ZrC-SiC multi-coating as outer layer and ZrC-SiC-PyC ceramics as inner matrix was formed. ZrC and SiC rich areas were formed in the composites and on the coating surface due to the formation of Zr-Si intermetallic compounds in the RMI process. Mechanical tests showed that the average compression strength of the C/C-ZrC-SiC composites was 133.86 MPa, and the carbon fibers in the composites were not seriously damaged after the RMI process.

Fabrication and microstructure of ZrB_2–ZrC–SiC coatings on C/C composites by reactive melt infiltration using ZrSi_2 alloy

ZrB_2–ZrC–SiC ternary coatings on C/C composites are investigated by reactive melt infiltration of ZrSi_2 alloy into pre-coatings. Two different pre-coating structures, including porous B_4C–C and dense C/B, are designed by slurry dip and chemical vapor deposition(CVD) process respectively. The coating prepared by reactive melt infiltration(RMI) into B_4C–C presents a flat and smooth surface with a three-layer cross-sectional structure, namely interior SiC transition layer, gradient ZrB_2–ZrC–SiC layer, and ZrB_2–ZrC exterior layer. In comparison, the coating prepared by RMI into C/B shows a more granular surface with a different three-layer cross-sectional structure, interior unreacted B–C pre-coating layer, middle SiC layer, and exterior ZrB_2–ZrC–ZrSi_2 layer. The forming mechanisms of the specific microstructures in two coatings are also investigated and discussed in detail.

Microstructure and Mechanical Properties of ZrC_(x)-NbC_(y)-Cu Composites by Reactive Infiltration at 1300℃

ZrC_(x)-NbC_(y)-Cu composites were fabricated by pressure-less reactive infiltration of Zr-Cu binary melts into porous NbC preforms at 1300℃.The effect of Zr content in the infiltrator on microstructure of the as-synthesized composites was studied.Mechanical properties of the composites were reported.A partial displacement of Nb atoms in NbC by Zr atoms from Zr-Cu melt occurs during the reaction between Zr-Cu melt and porous NbC preform.The formation of a core-shell structure suggests the reaction is mainly a dissolutionprecipitation type.NbC dissolves into Zr-Cu melt,from which the(Nb,Zr)C_(z)phase precipitates and grows.With increasing Zr content in the Zr-Cu infiltrator,the reaction is enhanced and the infiltration is easily chocked.ZrC_(x)-NbC_(y)-Cu composite is synthesized using Zr_(14)Cu_(51)infiltrator.The flexural strength and fracture toughness of ZrC_(x)-NbC_(y)-Cu composite reach 637 MPa and 12.7 MPa·m^(1/2),respectively.And the improved toughness is probably attributed to residual Cu phase and plate-like Nb_(x)C_(y)phases.

Reaction mechanism and microstructure development of ZrSi_(2) melt-infiltrated C_(f)/SiC-ZrC-ZrB_(2) composites:The influence of preform pore structures

Reactive melt infiltration(RMI)is an effective method for fabrication of highly dense carbon fiber reinforced ultra-high temperature ceramic matrix composites(Cf/UHTCs).In this work,C_(f)/SiC-ZrC-ZrB_(2)composites were fabricated by infiltrating ZrSi_(2)melt into porous C_(f)/B_(4)C-C preforms,where the physical and chemical reactions involved during the RMI process were identified and analyzed.Inhomogeneous infiltration between the inter-and intra-bundle pores was revealed,and was found to be strongly related to the pore structures of the C_(f)/B_(4)C-C preform.It is indicated that the inhomogeneous infiltration can be mitigated remarkably with increasing porosity and pore size of the preform.The effect of pore size on the RMI process was also investigated by a quantitative model,which agrees very well with the experiment results.It further indicates that the inhomogeneous infiltration can also be relieved at elevated RMI temperature.However,excessive infiltration at elevated temperature or more porous preform may cause serious erosion on interphase and fibers,leading to mechanical properties deterioration of the final composites.