CN115747742A - A preparation method of high-hardness high-entropy alloy film with grain size gradient - Google Patents

Abstract

The invention discloses a preparation method of a high-hardness high-entropy alloy film with grain size gradient, which is characterized in that a magnetron sputtering film is utilized to prepare a film with structural heterogeneity in the thickness direction, and then crystallization is regulated and controlled through low-temperature annealing, so that the high-hardness film with the grain size gradient is obtained.

Description

A preparation method of high-hardness high-entropy alloy film with grain size gradient

technical field

The invention belongs to the field of alloy materials, and in particular relates to a preparation method of a high-hardness high-entropy alloy thin film with a grain size gradient.

Background technique

In 2004, once the concept of high-entropy alloys was proposed, it attracted the attention of many scholars. It broke the design restrictions of traditional alloys, abandoned the distinction between solvent and solute in alloys, and has the structural characteristics of multiple principal elements. Among them, CrMnFeCoNi high-entropy alloys with stable FCC single-phase structure characteristics have been widely studied because of their excellent comprehensive mechanical properties such as excellent low-temperature performance and high creep resistance, but they still inevitably have strong plasticity conflicts, namely Characteristic of high plasticity but low strength. For example, the ductility of CrMnFeCoNi is 60-70%, and the fracture toughness exceeds 200MPa/m, but its strength at room temperature needs to be further improved.

For FCC single-phase metals, in order to increase its strength without losing its ductility, or even simultaneously improve the ductility to achieve the synergistic effect of strength and ductility, it is necessary to carry out structural design. Reasonable structural design is an effective means to break the single-phase strong-plastic conflict of FCC. Among them, the grain size gradient is considered to be an effective structure design, and a reasonable gradient structure design can take both strength and plasticity into account. For bulk materials, a variety of surface mechanical treatments, such as shot peening, high-pressure torsion, etc., can be used to make the surface structure nanoscale, and then obtain the transition from surface nanocrystals to internal coarse grain size gradient structure. The good combination of nanocrystalline strength and macrocrystalline plasticity can improve the strength of FCC phase structure materials without premature failure. However, the material thickness of the thin film system is generally micron-scale, the grain size is mostly nano-scale, and the structure is hard and brittle, so it is difficult to design structural gradients through mechanical processing. Therefore, the research on thin film systems is mostly structural composite (multilayer film) or composition design (element addition), but there are still difficulties in gradient structure design. How to achieve feasible grain size gradient structure design and effectively improve the strength of FCC single-phase alloys in high-entropy alloy thin film systems is challenging.

Contents of the invention

Based on the above discussion, the present invention aims to propose a method for preparing a high-hardness high-entropy alloy film with a grain size gradient.

To achieve the above object, the present invention adopts the following technical solutions:

A method for preparing a high-hardness high-entropy alloy thin film with a grain size gradient. The thin film is obtained by magnetron sputtering and co-sputtering, and the high-entropy alloy thin film whose grain size continuously changes along the thickness direction is obtained through low-temperature annealing control.

The method adopted in the present invention specifically comprises the following steps:

1) After ultrasonic cleaning in alcohol for 5-10 minutes, the single-sided polished single-crystal silicon substrate and the bottom bracket are fixed diagonally, and then inserted horizontally (polished side up) into the ultra-high vacuum magnetron sputtering equipment;

2) Fix the alloy target to be sputtered and the pure metal target on the RF and DC power sources respectively;

3) After the combination of mechanical pump and molecular pump is used to pump to the required high vacuum condition, high-purity argon gas is introduced as the main ionized gas for glow discharge;

4) After confirming the gas flow, adjust the two power controllers to the required power, turn on the power, and start pre-sputtering for 20-30 minutes to remove impurities on the target surface;

5) After the pre-sputtering is over, use the control lever to flip the substrate (polished side down) to start formal co-sputtering, and turn on the 360°rotation control switch to ensure sputtering uniformity;

6) Place the deposited alloy film in a vacuum annealing furnace, keep it at 395-405°C for 60 minutes, and then turn off the heating to cool the sample.

The high vacuum means that the degree of vacuum needs to be as low as 7x10 ^-4 Pa or below.

The purity of the high-purity argon gas is ≥99.999%.

During the sputtering process, the power of the RF power supply is fixed (>100W), while the power of the DC power supply varies from large to small (0-30W).

Further, during step 6) during the annealing process, the timing starts when the temperature display reaches 400°C. In the early stage of cooling, it is necessary to control the cooling rate to 10°C/min, and start cooling with the furnace after reaching 200°C.

The present invention has the following advantages:

1. Using this method to obtain samples with gradient changes in the size of nanocrystalline grains along the thickness direction of the high-entropy alloy film.

2. The structural design of the gradient change in grain size makes the hardness of CrMnFeCoNi high-entropy alloy with FCC single-phase structure reach 13.52GPa.

Description of drawings

Figure 1 is a cross-sectional TEM structure diagram of the film;

(a) The overall cross-sectional view (thin area) of the TEM sample.

(b) High-resolution microstructure at "1" in Figure (a)

(c) High-resolution microstructure at "2" in Figure (a)

(d) High-resolution microstructure at "3" in Figure (a)

Figure 2 is the TEM selected area diffraction pattern and calibration results of the high-entropy alloy thin film.

Fig. 3 is a comparative diagram of hardness of CrMnFeCoNi-based FCC phase nanocrystals.

Detailed ways

The present invention will be described in detail below in conjunction with specific examples and accompanying drawings, but it is not intended to limit the present invention.

Referring to Figure 1, Figure (a) shows the overall cross-sectional view of the thin area after TEM sample preparation of the high-entropy alloy thin film, showing that the thickness of the film is about 1.8 microns, and Figures (b-d) show enlarged views of the microstructure of different areas, dotted lines A change in grain size is shown, ie a grain size transition from greater than 30 nm to about 5 nm. "1" is near the surface.

Referring to Figure 2, the thin film phase structure shown in the diffraction pattern is still labeled as FCC single-phase nano-polycrystalline.

Referring to Figure 3, when the hardness of the film is compared with that of other CrMnFeCoNi-based FCC single-phase nanocrystals, the hardness of this film has obvious advantages.

Example 1

A 5-element non-isoatomic ratio high-entropy alloy thin film composed of CrMnFeCoNi was prepared by magnetron co-sputtering. CrMnFeCoNi high-entropy alloy target and pure manganese metal target with near-equal atomic ratio were co-sputtered and placed on the RF power supply and DC power supply respectively. The total shooting time is 4 hours. Then anneal at 400°C for 60min in a vacuum annealing furnace, and control the cooling rate to 10°C/min after the heat preservation is over.

The TEM characterization results of the obtained high-entropy alloy thin film are shown in Figure 1. The results show that the structure of the thin film has a nanocrystalline grain size gradient, and the grain size on the surface is greater than 30nm. As the thickness increases, the grain size transitions to about 5nm in the interior. . The phase structure remains as FCC single phase (as shown in Figure 2). Compared with other high-entropy alloy films, the film prepared by the present invention has outstanding high hardness (13.52GPa), and compared with other single-size FCC single-phase nanocrystalline films, the hardness is outstanding.

Example 2

Through magnetron sputtering, control the RF power supply and DC power supply at the same time to sputter CrMnFeCoNi high-entropy alloy targets and pure manganese metal targets with nearly equiatomic ratio. The power of RF power supply is still stable at 120W, and the power of DC power supply is from 4W Change to 30W for a total sputtering time of 4 hours. Then anneal at 400°C for 60min in a vacuum annealing furnace, and control the cooling rate to 10°C/min after the heat preservation is over.

The resulting high-entropy alloy film was characterized by nano-indentation hardness of 13.37GPa. However, there is no change in grain size in the structure, showing a composite structure of crystalline/amorphous phases.

Example 3

Through magnetron sputtering, the RF power supply and the DC power supply are simultaneously controlled to sputter CrMnFeCoNi high-entropy alloy targets and pure manganese metal targets with near equiatomic ratios. The power of the RF power supply is stable at 120W, and the power of the DC power supply is controlled at 10W. , the total sputtering time is 4 hours. Then anneal at 400°C for 60min in a vacuum annealing furnace, and control the cooling rate to 10°C/min after the heat preservation is over.

The resulting high-entropy alloy film was characterized by nano-indentation hardness of 8.008GPa. However, there is no change in grain size in the structure, showing a composite structure of crystalline/amorphous phases.

Claims (8)

1. A method for preparing a high-hardness high-entropy alloy thin film with a grain size gradient, characterized in that: utilize a magnetron sputtering thin film to prepare a thin film with structural heterogeneity in the thickness direction, then adjust and control crystallization by low-temperature annealing, and then Obtaining a high-hardness film with a grain size gradient specifically includes the following steps: 1) After ultrasonic cleaning in alcohol for 5-10 minutes, the single-sided polished single-crystal silicon substrate and the bottom bracket are fixed diagonally and then inserted horizontally, with the polished side facing up, into the ultra-high vacuum magnetron sputtering equipment; 2) Fix the high-entropy alloy target and the pure metal target to be sputtered on the RF and DC power sources respectively; 3) After the combination of mechanical pump and molecular pump is used to pump to the required high vacuum condition, high-purity argon gas is introduced as the main ionized gas for glow discharge; 4) After confirming the gas flow, adjust the two power controllers to the required power, turn on the power, and start pre-sputtering for 20-30 minutes to remove impurities on the target surface; 5) After the pre-sputtering is over, use the control lever to turn the polished side of the substrate down to start the formal co-sputtering, and turn on the rotary control switch to ensure the uniformity of sputtering; 6) Place the deposited alloy film in a vacuum annealing furnace, hold it at 395-405° C. for 60 minutes, and then turn off the heating to cool the sample to obtain a high-hardness film with a grain size gradient. 2. The preparation method according to claim 1, characterized in that: high vacuum means that the degree of vacuum needs to be as low as 7x10 ^-4 Pa or below. 3. The preparation method according to claim 1, characterized in that: the purity of the high-purity argon is ≥99.999%. 4. The preparation method according to claim 1, characterized in that: during the co-sputtering process, the power of the RF power supply is fixed >100W, while the power of the DC power supply varies from large to small by 0-30W. 5. The preparation method according to claim 1, characterized in that: the cooling rate needs to be controlled at 9-11°C/min in the early stage of cooling, and the furnace cooling starts after reaching 195-200°C. 6. The preparation method according to claim 1, characterized in that: the surface grain size of the prepared high-entropy alloy thin film is greater than 30nm, and as the thickness increases, the grain size transitions to the inner 4-6nm, and has a thickness of 13.52 High hardness of GPa. 7. The preparation method according to claim 1, characterized in that: in step 5), it is a 360° rotation control switch. 8. The preparation method according to claim 1, characterized in that: the required power in step 4) is 0-120W.

Images