Evaluation of the hardness and Young's modulus of electrodeposited Al–W alloy films by nano-indentation

Abstract

14Al-W alloy films with various W contents up to ~12 at% were prepared by 15 electrodeposition using 1-ethyl-3-methylimidazolium chloride (EMIC)-AlCl3 ionic 16 liquids with different concentrations of W precursor, W6Cl12. The hardness (H) and 17 Young's modulus (E) of the films were examined by nano-indentation. The films were 18 composed of a single-phase fcc Al super-saturated solid solution, an amorphous phase, or 19 both, depending on the W content and the deposition conditions. The H value increased 20 with increasing W content up to 9.8 at% and then decreased slightly with further increases 21 in the W content up to 12.4 at%. A similar trend was observed in the E value with 22 increasing W content, but the decrease in E value at 12.4 at% W was more significant than 23 that in H value. The changes in the H and E values are discussed from the viewpoints of 24 the grain size and the constituent phases. The 9.8-12.4 at% W films, which had relatively 25 high H values and H/E ratios, are expected to have a higher resistance to mechanical 26 damage than Al films.27 28 Keywords 29 Electroplating, Ionic liquid, Nano-indentation, Amorphous alloy, Aluminum, Tungsten 30 31 2 1 1. Introduction 2 Al metal shows high oxidation and corrosion resistance because of the thin passive film 3 on its surface. Thus Al metal films have attracted much research attention as corrosion-4 protective coatings on reactive materials such as a Mg alloy [1,2]. However, if exposed 5 to an environment containing halide anions such as Cl − , the passive film on Al metal is 6 destroyed locally, followed by pitting corrosion [3]. The resistance of Al metal to pitting 7 corrosion is enhanced by alloying with other transition metals [3]. Among Al alloys, Al-8 W alloys are known to exhibit significant resistance to pitting corrosion [3,4]. Therefore, 9 the formation of Al-W alloy films was intensively studied. 10 The formation of Al-W alloy films by sputtering [4-15], ion implantation [16], laser 11 surface alloying [17], and electrodeposition [18-22] was reported. Of these methods, 12 electrodeposition has particular advantages in that a thick film can be formed over a large 13 area relatively quickly by means of simple equipment. The electrodeposition of Al-W 14 alloys with high W contents was achieved using a 1-ethyl-3-methylimidazolium chloride 15 (EMIC)-AlCl3 ionic liquid containing potassium tungsten(III) chloride, K3W2Cl9 [18-16 20]. However, alloys with more than 5 at% W obtained from this bath showed a powdery 17 morphology. The morphology was improved by changing the W precursor from K3W2Cl9 18 to tungsten(II) chloride, W6Cl12 [22]. We reported that dense Al-W alloy films with up to 19 ~12 at% W can be electrodeposited from an EMIC-AlCl3 ionic liquid containing W6Cl12 20[22]. The Al-W alloy films obtained from this bath were composed of a super-saturated 21 fcc Al solid solution with W contents lower than ~9 at%, and with an amorphous phase 22

Electrodeposition of Aluminum–Tungsten Alloy Films Using EMIC–AlCl₃–W₆Cl₁₂ Ionic Liquids of Different Compositions

“…44,45) We have previously examined AlW alloy films with up to ³12 at% W for hardness and Young's modulus, and showed that these alloy films are harder and have a higher ratio of hardness to Young's modulus than Al metal. 16) This study suggested that AlW alloy films with a higher W content could have an even higher mechanical strength.…”

“…The prepared EMICAlCl 3 melt was stored in a 25-mL glass vessel used as an electrolytic cell. W 6 Cl 12 was synthesized by a method described in our previous report, 15,16) and was added to the melt maintained at 80°C throughout the experiment. The bath temperature was controlled by a thermostat (TJA-550, AS ONE) connected to a rubber heater wound around the cell and a thermocouple immersed in the bath.…”

“…However, AlW alloy films with W contents higher than ³12 at% could not be electrodeposited using EMIC 2AlCl 3 W 6 Cl 12 baths. 16) The W content of the alloy films electrodeposited at a constant current density increased linearly up to ³12 at% with increasing W 6 Cl 12 concentration of the bath in a low W 6 Cl 12 concentration range, but the W content of the films saturated at ³12 at% at a higher W 6 Cl 12 concentration. Potentiostatic electrodeposition at various potentials in an EMIC2AlCl 3 bath saturated with W 6 Cl 12 also failed to yield alloy films with >³12 at% W. 15) One of the parameters that have not yet been explored in this system is the AlCl 3 /EMIC molar ratio of the bath.…”

“…In contrast, when the W precursor was replaced with tungsten(II) chloride, W 6 Cl 12 , dense AlW alloy films with up to ³12 at% W were successfully electrodeposited. 15,16) The resultant dense films were confirmed to exhibit a good corrosion resistance.…”

Insight into indentation-induced plastic flow in austenitic stainless steel

“…Nanoindentation has become a mature technique for mechanical property identification and small lengthscale materials science research [1][2][3][4][5][6][7][8][9][10][11][12][13]. The load versus penetration depth curve (P-h curve) is used to determine the elastic modulus and hardness via the Oliver-Pharr method [4,5,14,15]. Indentation pop-in load is the force which the indentation transitions by a depth jump from the elastic to the elastoplastic regime.…”