Preparation and characterization of continuous high-temperature resistant Si-Al-C fibers by one-step method

Abstract

Using polymer-derived technology, continuous high-temperature resistant Si-Al-C fibers were prepared by one step method, which included melt-spinning of polyaluminocarbosilane (PACS), curing of continuous PACS fibers, and sintering of the cured products. The results show that the average diameter and tensile strength of continuous Si-Al-C fibers are 11 to 12 μm and 1.8 to 2.0 GPa, respectively. The chemical formula of Si-Al-C fibers is SiC 1.01 O 0.040 0Al 0.024 , which is nearly stoichometric.The fibers are mainly composed of β-SiC crystalline, small amount of α-SiC, and amorphous SiC. Continuous Si-Al-C fibers exhibit excellent thermal stability. When the fibers were exposed in argon for 1 h, the tensile strength did not decrease until 1500℃. After heat treatment at 1800℃ in argon for 1 h, the fibers maintained about 80% of the initial strength. It was higher than that of Nicalon and Hi-Nicalon fibers.high-temperature resistant, continuous Si-Al-C fibers, one step method, polymer-derived technology Silicon carbide (SiC) fibers, which have high tensile strength, high elastic modulus, good thermal stability, and oxidation resistance, are one of the best candidates of the reinforcements available for continuous-fiber-reinforced ceramic-matrix composites (CMCs) [1] . Polymer-derived technology is one of the main methods to produce continuous SiC fibers [2,3] . It includes four steps: synthesis of polycarbosiane (PCS), melt-spinning, curing of continuous PCS fibers, and pyrolysis of the cured products. But, one problem of those fibers such as Nicalon is that thermo-mechanical stability is good only below 1200℃. The major mechanism of the thermal degradation of SiC fibers has been reported to be the oxidation of silicon and carbon to form volatile CO and SiO products, which eventually develops a porous microstructure in the fibers [4,5] .Recently, several attempts have been made in order to improve the mechanical properties and thermal stability of these fibers. One of the methods is to prepare continuous SiC fibers including hetero-elements through the physical or chemical modification of precursor [6] . For example, the

Cerium Addition Improves Cleanliness and Refines Microstructure of As‐Cast High‐Nitrogen Stainless Bearing Steel

“…Similarly, MgO inclusions could not form because the formation of numerous Ce 2 O 2 S inclusions further consumed [O], and [Mg] would react with [N] as follows: [ 61 ] …”

“…Afterward, the generated [Mg] would also react with the residual [O] to form MgO inclusions: [13] ½Mg þ ½O ¼ MgOðsÞ (8) Furthermore, the mass fraction of MnS decreased from 0.00187 to 0.00114 wt%. It should be pointed out that owing to the low formation temperature of MnS, the reduction of MnS inclusion was not due to its reaction with [Ce] reacted with [N] to form CeN inclusions as follows: [60] ½Ce þ ½N ¼ CeNðsÞ (9) Similarly, MgO inclusions could not form because the formation of numerous Ce 2 O 2 S inclusions further consumed [O], and [Mg] would react with [N] as follows: [61] 3½Mg þ 2½N ¼ Mg 3 N 2 ðsÞ (10) The mass fraction of Mg 3 N 2 was only 0.00029 wt% as a result of the low Mg content (0.0004 wt%) in 0.020Ce steel. Therefore, the types of inclusions in 0.020Ce steel were further changed into Ce 2 O 2 S, Ce 2 O 3 , CeN and Mg 3 N 2 .…”