| Fe-based amorphous/nanocrystalline alloys usually have excellent mechanical, softmagnetic properties and relatively low cost, which may have a wide application as bothstructural materials and functional materials. However, Fe-based amorphous alloys also havesome disadvantages, such as the harsh preparation conditions, low glass forming ability, andlack of ductility at room temperature, which have greatly limited the widespread applicationof Fe-based amorphous alloys. Therefore, it is of great significance to develop some newkinds of bulk Fe-based amorphous alloy and nanocrystalline composite material withexcellent mechanical properties.The chemical composition of amorphous alloy was designed according to the threeprinciples of Inoue and modulus criterion, etc. Fe100-x(NbTiTa)x(x=20,30,40) was finallyselected for the study. We used mechanical alloying (MA) and spark plasma sintering (SPS)technique to prepare Fe-based amorphous/nanocrystalline alloys. The structure evolution,amorphization, crystallization kinetics and the differences of glass forming ability wereinvestigated. Then we chose the one with the highest glass-forming ability among the threepowders and consolidated to bulk Fe-based alloys by SPS. The influences of differentsintering parameters, such as sintering temperature, holding time, on the microstructure andmechanical properties of sintered samples were investigated. In addition, the amorphouspowder was added to pure iron powder in order to get Fe-based amorphous/nanocrystallinecomposite materials of high performance.Firstly, amorphous Fe100-x(NbTiTa)x(x=20,30,40) alloy powders without metalloidswere synthesized from commercially available pure elemental powders by mechanicalalloying. Microstructure, glass-forming ability, thermal stability and crystallization kinetics ofthe as-milled powders were analyzed by SEM, XRD, DSC and TEM. Results show thatFe60(NbTiTa)40has the best glass forming ability with ΔTx=101K, which could be explainedby appropriate atomic-size mismatch and large negative heat of mixing among mainconstituent elements. The non-isothermal crystallization kinetics were analyzed. The values ofthe Avrami exponent (n) suggest that the crystallization of Fe60(NbTiTa)40andFe70(NbTiTa)30amorphous alloy powders is governed by volume diffusion-controlled two-dimensional growth and three-dimensional growth, respectively. The materials obtainedin this research provide good candidate for fabricating bulk Fe-based amorphous alloys andrelated bulk nanocrystalline materials through powder metallurgy methods.Secondly, Fe60(NbTiTa)40was chosen to be milled by using QM-2SP2. Bulk Fe-basedalloys were synthesized by SPS. The results show that when the amorphous powder wassintered at relatively low temperature with high pressure, the amorphous powder partiallycrystallized and the sintering process has not been completed, which results in the low relativedensity. The compression strength of the sample is only about484MPa. When the amorphouspowder was sintered at high temperature with relatively low pressure, the Fe60(NbTiTa)40amophous powder all crystallized, forming some new phases. The sintering temperature has agreater impact on the microstructure and mechanical performance, the compressive strengthof the sintered samples gradually increased with increasing sintering temperature. when thesintering temperature is1100℃, the fracture strength is about1803MPa. Holding time alsohave a great influnce on the strength of the sintered samples. when the holding time is10min,the fracture strength of the sintered sample reaches2334MPa. In addition, all the sinteredsamples show brittle fracture under compression, no macroscopic plastic deformation wereobserved..Finally, Fe60(NbTiTa)40/Fe mixed powder were consolidated by SPS in order to getFe-based amorphous/nanocrystalline composite materials. Results show that sinteringtemperature has a great impact on the microstructure and mechanical properties of the sinteredsamples. When the sintering temperature was750℃, Fe60(NbTiTa)40didn’t crystallize.When the sintering temperature was800℃，the amorphous powder partly crystallized.Fe60(NbTiTa)40powder plays the role of dispersion strengthen in Fe-matrix and leads to theincrease of the iron powder compression strength. The compression strengths reach1460MPaand1295MPa, respectively. When the sintering temperature continues to rise, Fe60(NbTiTa)40completely crystallized. The sintered samples exhibited ultrahigh plastic deformation abilityand didn’t fracture at room temperature but were pressed into drum-shaped. The content ofFe60(NbTiTa)40has a great influence on the compression strength, the strength increases withthe increased content of Fe60(NbTiTa)40, and no significant effect on the plastic ability. Theholding time also effect the properties of the samples. The maximum compressive strength of the material is about520MPa when sintered at900℃and holding for5min, continues toextend the holding time, the yield strength of the material decreases because of the crystallinegrows. |
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