【摘要】 利用XRD,SEM,TEM等实验方法,研究了铝热合成法制备的FeNiCrAl合金的微观组织,并研究了铝热剂成分中Al含量对合金拉伸性能的影响.结果表明,当铝热剂中Al含量不超过25.4%(质量分数)时,合金的主要组成相是奥氏体;当铝热剂中Al含量达到26.6%时,合金主要组成相为铁素体,同时析出颗粒状的NiAl相;随着Al含量继续增加,颗粒状析出相逐渐被编织状组织所取代.编织状组织的产生是液相调幅分解的结果.铝热剂中Al含量的增加,会降低合金的断后延伸率.当铝热剂中Al含量为26.6%时,合金的抗拉强度达到最大,为640.87MPa.更多还原

【Abstract】 The excellent thermal conductivity, low thermal expansion and high oxidation resistance of ferritic FeNiCrAl alloys, provide them with the potential to be replacements for nickel-based superalloys in high-temperature applications. However, their usage is limited, because of their poor high- temperature mechanical properties.The high melting point of NiAl intermetallic compounds, together with their excellent high temperature stability and similar lattice parameters to a-Fe, allow them to be used to coherently strengthen ferritic FeNiCrAl alloys to extend their high-temperature performance. Traditionally, these Fe(Ni, Cr)/NiAl alloys are prepared by vacuum reaction melting followed by an aging process. But the aging process has drawbacks including excessive cost, the length of aging time required and coarsening of the NiAl phase at high temperature. A more cost-effective thermite reaction process, was tried to prepare the Fe(Ni, Cr)/NiAl alloys. In this route, ferrite FeNiCrAl alloys were strengthened by a high volume fraction nanoscale-NiAl phase which was achieved without using the aging process.Several types of thermites were designed and studies were conducted to explore the transformations of the alloy microstructures and the changes of the tensile properties with the various thermite compositions. The microstructures of these thermites synthesized Fe(Ni, Cr)/NiAl alloys were investigated using XRD, SEM, EDS, TEM and SAED.The effect of Al content in the thermites on the microstructures of the alloys was studied. Experimental results showed that when the thermites contained no more than 25.4%(mass fraction) of Al, the synthesized Fe(Ni, Cr)/NiAl alloys were composed primarily of an austenite phase. The main component phase of the alloy composites was transformed into ferrite when the mass fraction of Al in the thermites was 26.6%, meanwhile the NiAl particle precipitates arose. As the Al content of the mixture was further increased, the NiAl precipitates were gradually replaced by an intertexture structure. The intertexture structure was totally dominant when the mass fraction of Al in the thermites was 31.4%. Experimental results showed that this intertexture microstructure material was composed of a ferritic FeNiCrAl matrix with a width of 80~100 nm and NiAl precipitates with a width of about 50 nm, and the two phases matched coherently. This microstructure resulted from liquid spinodal decomposition. The effect of Al content on the mechanical properties of the alloys was also investigated. The increase of the Al content in the thermites resulted in a decrease of the elongation of the alloys, which varied from 25.5% to 1.7% when the mass fraction of Al ranged from 24.2% to 29.0%. When the thermites contained 26.6% mass fraction of Al, the tensile strength of the alloy achieved its maximum value of 640.87 MPa.更多还原