Dingqiang Li

Study of superplastic deformation in an FeAl based alloy with large grains

In this paper some results of studies on a superplastically deformed FeAl based alloy are reported. The tensile behavior of the FeAl based alloy Fe-36.5Al-2Ti (in atomic percent) under different strain rates at high temperatures was examined by optical microscopy. The results revealed that the FeAl based alloy with the grain size of 350 {micro}m exhibited a large elongation of more than 140% at 900 C and 1,000 C under a strain rate range of 1.39{times}10{sup {minus}4}/s{approximately}2.78{times}10{sup {minus}2}/s. The maximum elongation is 208% at 1,000 C under a strain rate of 1.39{times}10{sup {minus}2}/s. The reason for the large elongation is ascribed to the dynamic recovery and recrystallization in this alloy during deformation at high temperatures.

Superplasticity in large-grained FeAl-based intermetallic alloys

Abstract The superplastic behavior of Fe-36.5Al, Fe-36.5Al-1 Ti and Fe-36.5Al-2Ti alloys with large grains has been investigated. The large grained FeAl alloys exhibit all deformation characteristics of conventionally fine-grained superplastic alloys. The values of strain rate sensitivity index, m are all larger than 0.3 at a temperature range of 900 to 1000 °C and a strain rate range of 2.08 × 10−4 s−1 to 4.16 × 10−2s−1, at which the superplastic deformation proceeds. The maximum elongation to fracture of 300% with m value of 0.34 is obtained for Fe-36.5Al-2Ti alloy deformed at 1000 °C under an initial strain rate of 2.08 × 10−2 s−1. The superplastic phenomenon is attributed to continuous recovery and recrystallization.

Cyclic Deformation Behavior of a Rare-Earth Containing Extruded Magnesium Alloy: Effect of Heat Treatment

The present study was aimed at evaluating strain-controlled cyclic deformation behavior of a rare-earth (RE) element containing Mg-10Gd-3Y-0.5Zr (GW103K) alloy in different states (as-extruded, peak-aged (T5), and solution-treated and peak-aged (T6)). The addition of RE elements led to an effective grain refinement and weak texture in the as-extruded alloy. While heat treatment resulted in a grain growth modestly in the T5 state and significantly in the T6 state, a high density of nano-sized and bamboo-leaf/plate-shaped β′ (Mg7(Gd,Y)) precipitates was observed to distribute uniformly in the α-Mg matrix. The yield strength and ultimate tensile strength, as well as the maximum and minimum peak stresses during cyclic deformation in the T5 and T6 states were significantly higher than those in the as-extruded state. Unlike RE-free extruded Mg alloys, symmetrical hysteresis loops in tension and compression and cyclic stabilization were present in the GW103K alloy in different states. The fatigue life of this alloy in the three conditions, which could be well described by the Coffin–Manson law and Basquin’s equation, was equivalent within the experimental scatter and was longer than that of RE-free extruded Mg alloys. This was predominantly attributed to the presence of the relatively weak texture and the suppression of twinning activities stemming from the fine grain sizes and especially RE-containing β′ precipitates. Fatigue crack was observed to initiate from the specimen surface in all the three alloy states and the initiation site contained some cleavage-like facets after T6 heat treatment. Crack propagation was characterized mainly by the characteristic fatigue striations.

The microstructural evolution during superplastic deformation in FeAl intermetallic compound

The intermetallic compound FeAl has received a great deal of attention during the past few years because of its excellent oxidation resistance, retention of good strength to intermediate temperatures and its low density compared with most iron or nickel-based alloys. Superplasticity has been discovered in some intermetallics with fine grain size, such as Ni{sub 3}Al and Ni{sub 3}Si, Ti{sub 3}Al and TiAl. Recently, some work on the phenomenon of superplasticity in Fe{sub 3}Al and FeAl-based alloys has been reported. A FeAl based-alloy with a grain size of above 350 {micro}m exhibited an elongation of more than 150% at 900 {approximately} 1,000 C in air. The maximum elongation of 208% was obtained at 1,000 C under a strain rate of 1.39 {times} 10{sup {minus}2}/s. The index of strain rate sensitivity, the m value, was in a range from 0.25 to 0.42(4). In this paper the dislocation features in an FeAl-based alloy after superplastic deformation, which have been investigated by transmission electron microscopy (TEM), are presented and the microstructural evolution during superplastic deformation is discussed.

Effect of temperature on the tensile properties and dislocation structures of FeAl alloys

Abstract Tensile deformation and fracture behavior of three B2 structural intermetallic FeAl alloys—one binary alloy (Fe–36.5Al) and two ternary alloys (Fe–36.5Al–5Cr and Fe–36.5Al–2Ti)—were investigated at different temperatures between room temperature and 1000°C. The specimens were prepared by hot-rolling of ingots and heat treatment. The elongation to failure of the alloys was found to increase when the testing temperature increased from room temperature to 300°C, decrease slightly from 300 to 500°C, and increase dramatically from 600 to 1000°C. On the other hand, the yield strength of the alloys decreased slowly until 500°C, then increased slightly, and decreased dramatically between 700 and 1000°C. The abnormal yield effect of these alloys occurred in the temperature range 500–700°C. The addition of chromium or titanium was found to improve the tensile properties of FeAl alloys, especially at elevated temperatures (800–1000°C). The ternary Fe–36.5Al–5Cr or Fe–36.5Al–2Ti alloy had a higher elongation and higher yield strength than the binary Fe–36.5Al alloy. The fracture modes of these alloys when deformed at room temperature are a mixture of intergranular fracture and transgranular cleavage. With increase in temperature, the percentage of transgranular fracture generally increased, except for that observed around 500°C. Dislocations with a 〈111〉 Burgers vector are found in the FeAl alloy deformed at higher temperatures. It is suggested that the good ductility of the FeAl alloys deformed at higher temperatures may result from glide as well as climb of the dislocations with a 〈111〉 Burgers vector during deformation.

Microstructure evolution and activation energy during superplastic deformation of FeAl based intermetallics

At the temperature range from 875 C to 1,000 C under an initial strain rate range of 10{sup {minus}4}s{sup {minus}1} to 10{sup {minus}1}s{sup {minus}1}, the flow activation energy of FeAl based alloys were measured to be 370kJ {center_dot} mol{sup {minus}1} for Fe-36.5A, 290kJ {center_dot} mol{sup {minus}1} for Fe-36.5Al-1Ti and 260kJ {center_dot} mol{sup {minus}1} for Fe-36.5Al-2Ti alloy. During the superplastic deformation, the new small grains were separated from the original larger deformed grains and the average grain size became much finer from above 500{micro}m before deformation to 50--85{micro}m after deformation to fracture. It is confirmed that a continuous recrystallization process took place and superplasticity may result in this process.

Effects of strain rate and manganese addition on room temperature ductility of FeAl

In this paper, the beneficial effect of a manganese addition on room temperature ductility of Fe-36.5Al alloys and the effect of strain rate on the tensile behavior of Fe-36.5Al alloys with and without manganese are shown. The results confirm that a manganese addition has a beneficial effect on the ductility of Fe-36.5Al alloy, without any significant change in the fracture mode. Also, the results indicate that the tensile properties, especially ductility, are sensitive to the strain rate, but the fracture modes are independent of strain rate and are mixed fracture modes.

MÖssbauer Study on B2 Intermetallic Compound Fe-40Al and its Mn or Ti Containing Alloys

The Mossbauer measurements at room temperature have been carried out on the B2 intermetallic compound Fe-40Al and its Mn or Ti containing alloys. The results show that all the Mossbauer spectra of Fe-40Al and its Mn or Ti containing alloys are approximately one-peak singlets. The Fe atoms in these alloys show no significant magnetic moment. The spectra of Mn or Ti containing alloys have been fitted with two Lorentzian lines by the method of least squares. By studying the isomer shifts and other parameters of these fitted lines, it have been shown that Mn atoms occupy both Fe and A1 sublattices, Ti atoms occupy preferentially Fe sublattice, however, a few of Ti atoms occupy A1 sublattice only as Ti concentration is over certain amount (∼5-at%).

The Phenomenon of Superplasticity in Feal-Ti Alloy with Large Grains

The phenomenon of superplasticity in an ordered FeAl based alloy is reported in this paper for the first time. The behavior of superplastic deformation for the FeAl based alloy (Fe-36.5at.%2at.%Ti) with large grains of above 300 {mu}m has been examined at 1,000 C in a strain rate range from 1.39 {times} 10{sup {minus}4}/s to 2.78 {times} 10{sup {minus}2}/s. The maximum elongation of 208% for the FeAl based alloy with large grains has been obtained and the index of strain rate sensitivity, the m value, has a range of values from 0.25 to 0.42. The reason for the large elongation is ascribed to the dynamic recovery and recrystallization during deformation in this large grained alloy at high temperatures.

The Mechanical Properties of Fe-36.5Al and its Cr or ti Containing Alloys at Elevated Temperature

The mechanical properties of B2 structural FeAl alloys, prepared by hot rolling, at elevated temperatures have been measured by tensile tests. The alloys of Fe-36.5at.%A1, Fe-36.5at.%A1-5at.%Cr and Fe-36.5at.%Al-2at.%Ti were taken for tensile tests at a temperature range from room temperature to 1000°C. The fracture surfaces of these alloys were observed by SEM. The results showed that elongations of these alloys increased with increasing temperature when the testing temperatures were above 600°C. All the maximum elongations of these alloys appeared at 1000°C and those of Fe-36.5A1, Fe-36.5Al-5Cr, and Fe-36.5Al-2Ti alloys were 120%, 183% and 208% respectively. Fracture surfaces showed that failure of these alloys was by a combination of intergranular fracture and transgranular cleavage below 700°C. but showed a ductile fracture above 700°C. The ductility and strength of ternary alloys were higher than that of binary FeAl alloy at elevated temperatures, especially at high temperature. The dislocations and helices have been observed in Fe-36.5A1 alloy by TEM. The large elongation of FeAl alloy at high temperature resulted from dislocations slipping and helices climbing.