Effect of Nickel and Titanium on Properties of Fe-Al-Si Alloy Prepared by Mechanical Alloying and Spark Plasma Sintering

Abstract

F.P.) 2 SVÚOM s.r.o., U Měšt'anského pivovaru 934/4, Abstract: This paper describes the structure and properties of an innovative Fe-Al-Si alloy with a reduced amount of silicon (5 wt. %) in order to avoid excessive brittleness. The alloy was produced by a combination of mechanical alloying and spark plasma sintering. Nickel and titanium were independently tested as the alloying elements for this alloy. It was found that wear resistance, which reached values comparable with tool steels, could be further improved by the addition of nickel. Nickel also improved the high-temperature oxidation behavior, because it lowers the liability of the oxide layers to spallation. Both nickel and titanium increased the hardness of the alloy. Titanium negatively influenced oxidation behavior and wear resistance because of the presence of titanium dioxide in the oxide layer and the brittle silicides that caused chipping wear, respectively. plasma sintering [16]. The alloys exhibited a very good oxidation resistance at high temperatures-much better than binary Fe-Al and Fe-Si alloys [17]. The improvement of oxidation resistance does not lie in the incorporation of silicon to the oxide layer in a significant amount; rather, it lies in the formation of large volume fraction of silicides under the oxide layer, when aluminum diffuse to the surface in order to form Al 2 O 3 . Additionally, it has been found that the presence of silicon reduces the amount of iron oxide in scales, causing their better adherence to a substrate due to a more favorable Pilling-Bedworth ratio [16]. However, the FeAl20Si20 alloy is very brittle. Powder metallurgy methods, including our high-energy mechanical alloying [18] and spark plasma sintering, allowed for an increase in the fracture toughness, but the values at room temperature still reached the parameters of brittle ceramics, i.e., approximately 3.5 MPa.m 1/2 [16]. Due to these parameters, the alloy could be applicable as a protective coating rather than as a bulk material.In recent research, we studied the high-temperature oxidation resistance of Fe-Al-Si alloys and its dependence on the Al:Si ratio, and we found that the 35:5 provided almost the same oxidation performance [17]. Since silicon is listed as a critical raw material in the EU [19], the minimization of its amount is reasonable. In a parallel research, our team studied Ti-Al alloys and proved that silicon also improves their oxidation behavior and reinforces the material by forming hard Ti 5 Si 3 silicides [20]. On the other hand, nickel is known to form stable aluminides rather than silicides [21].Therefore, this work aimed at a possible improvement of the properties of a lower-silicon FeAl35Si5 alloy by the addition of titanium as the expected silicide-forming element and nickel as the probable aluminide stabilizer. The tests were intended to study the high temperature oxidation behavior, basic mechanical properties, and tribological properties. Materials and Methods

The Effect of Simultaneous Si and Ti/Mo Alloying on High-Temperature Strength of Fe3Al-Based Iron Aluminides

“…The effect of different additives, titanium among others, on mechanical properties of Fe-Al-Si alloy prepared by mechanical alloying and spark plasma sintering was described in detail by Novak et al [ 25 ]. It was showed, inter alia, that titanium addition improves the hardness values significantly, mainly due to the presence of hard phases.…”

Novel High-Entropy Aluminide-Silicide Alloy

“…So we expected based on previous results that when the above-mentioned elements would be combined in equimolar proportions, we will obtain a highly substituted aluminide, silicide, or Fe-Al-Si based phase, where iron would be partially substituted by nickel and titanium. However, the latter possibility was considered as the less probable one, because both nickel and titanium decreased the amount of the ternary Fe-Al-Si phases in the mechanically alloyed materials [25]. In reality, the experiment led to the formation of a major amount of a phase, which was identified as the orthorhombic FeTiSi phase, being constituted by all used elements in approximately equimolar ratios.…”

“…The normal force acting on the ball was 5 N, and the total distance was 20 m. Since the material is relatively hard, we selected an aluminum oxide ball among the standardized materials used for this kind of test. These conditions were used in our previous works dealing with aluminide and silicide-based materials [21,25]. The profile and depth of the wear track were then measured using a DH-15 profilometer (Diavite, Bülach, Switzerland) with the skidless probe (Tribotechnic, Clichy, France) at three locations (approximately at 1 4 , 1 2 and 3 4 of the track length).…”

High-Temperature Corrosion Performance of FeAl-Based Alloys Containing Carbon in Molten Salt

“…Recently, it was reported that Ti addition together with carbon additions to FeAl-based alloys has successfully developed FeAl-based alloys with no graphite precipitation [12]. Addition of Ti to iron aluminides containing carbon leads to improvement in the mechanical properties [12,13], but it has been established that Ti could also improve the oxidation and corrosion resistance [14,15]. Li et al also found that Ti addition to Fe-36.5Al alloy leads to improvement of oxidation resistance due to compactness of oxide scales on the surface which deteriorate the further penetration of corrosive media [14,15].…”

“…Iron aluminide due to their better oxidation resistance at elevated temperature, are also considered as replacements of ferritic/austenitic steels for applications up to about 500 • C. Among iron aluminides, FeAl-based alloys with large amounts of Al (~37 wt.% or above) are generally considered potential candidate for protection at elevated temperature applications [15][16][17]. Ti additions to FeAl alloys with carbon to enhance its mechanical properties offers an excellent opportunity to improve its corrosion resistance especially supporting oxide adherence [14].…”