Keywords

1 Introduction

Bucket tooth is a very important part of excavator, and wear failure is the main failure form of bucket tooth [1]. The common methods to improve the surface wear resistance mainly include laser cladding, surfacing welding, thermal spraying, etc. Compared with the other surface modification measures, the coatings prepared by laser cladding technology have the advantages of dense structure and small dilution rate [2].

As an advanced surface strengthening technology, laser cladding technology has been widely used in the automobile industry [3]. It significantly improves the wear resistance and hardness of the substrate by depositing the cladding material onto the substrate [4]. This technology can strengthen the part and extend its service life, thereby reducing costs, improving economy and efficiency.

With the development of industry, single metal materials can no longer meet the production requirements, and their properties can be significantly improved by introducing reinforcing phases. There are two methods to introduce the enhanced phase: direct addition and in situ synthesis, in which the enhanced phase produced by the in-situ synthesis method is better matched to the substrate at the interface [5]. For example, Li [6] et al. synthesized TiB/TiC reinforced titanium-based composite coatings in situ on Ti–6Al–4V, and the coatings were free of porosity. Wang [7] et al. synthesized TiB-reinforced titanium-based composite coating in situ on Ti–8Al–1Mo–1V, and the results show that the TiB phase generated by in situ synthesis can effectively increase the hardness of the coatings.

In summary, the effects of different Ti, Nb and Cr3C2 powder ratios on the hardness and wear resistance of laser cladding (Ti, Nb)C reinforced nickel-based coating were studied to improve the wear resistance of bucket teeth, and the best powder ratio parameters were obtained.

2 Experimental Process

2.1 Experimental Materials and Parameters

The substrate is Q550 steel, and the specimen size is 100 mm × 100 mm × 12 mm. Nickel-based nickel alloy is used as the self-melting alloy powder, and different contents of Ti, Nb and Cr3C2 powders are added as the reinforcing phase powders. The specific configuration ratio of the powder is shown in Table 1. The laser cladding process parameters are shown in Table 2.

Table 1 Powder configuration ratio
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Table 2 The laser cladding process parameters
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2.2 Hardness Test

Hardness testing was used by HVST-1000Z hardness tester. The measuring load was 300 g and the measuring time was 10 s. Five points were randomly selected in the coatings for testing, and finally the average value was taken to obtain the microhardness.

2.3 Wear Test

MDW-05 high frequency reciprocating wear tester was used to carry out the wear test. The reciprocating stroke was 5 mm, the load was 50 N, and the test time was 30 min.

3 Results and Analysis

3.1 Microhardness

The microhardness of the cladding layer and substrate is shown in Fig. 1, the hardness of the substrate is 150 HV, and the hardness of the coating A to E is 206.2 HV, 205.7 HV, 218.5 HV, 210.2 HV, 213.4 HV, respectively. Overall increase in hardness of the coatings compared to the substrate. This is due to the fact that Cr can act as a solution strengthening effect.

Fig. 1
A column chart plots microhardness on the vertical axis. The estimated values are as follows. (A, 205), (B, 204), (C, 223), (D, 215), (E, 20), (substrate, 150).

Microhardness of the coatings and substrate

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3.2 Wear Resistance

Wear experiments were carried out on the coatings and the substrate, and the wear data are shown in Fig. 2. The wear amount of the substrate is 59.2 mg, and the wear amount of the coating A to E is 48.9 mg, 41.5 mg, 36.3 mg, 37.1 mg, 32.7 mg, respectively. The wear amount of the coatings E is much smaller than the coating A to D. The reason is that the content of Nb in powder E is much higher than that of other powders, and more NbC being generated during the laser cladding process, which improves the wear resistance of the coatings.

Fig. 2
A column chart plots wear mass loss on the vertical axis. The estimated values are as follows. (A, 49), (B, 42), (C, 37), (D, 39), (E, 35), (substrate, 60).

The wear amount of coatings and substrate

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The average friction coefficients of the substrate and coatings are shown in Fig. 3. The average friction coefficient of the substrate is 0.536, and the average friction coefficient of coatings A to E are 0.428, 0.499, 0.405, 0.481, 0.441, respectively.

Fig. 3
A column chart plots average friction coefficients on the vertical axis. The estimated values are as follows. (A, 0.43), (B, 0.5), (C, 0.4), (D, 0.5), (E, 0.45), (substrate, 0.55).

Average friction coefficients of cladded layers and substrate

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3.3 Wear Mechanism

The worn morphology under different Ti:Nb ratios is shown in Fig. 4. There are obvious furrows on the worn surface, indicating that the wear mechanism is mainly abrasive wear. Furthermore, there is a small amount of adhesive on the worn surface, indicating that there is slight adhesive wear. As can be seen from Fig. 5, the coatings did not undergo oxidative wear during the wear process.

Fig. 4
Ten microscopic views labeled a to j. A, c, e, g, and i feature smooth surfaces. B, d, f, h, and j display surfaces with more pronounced textures and have bright scattered particles on them.

Worn morphology of C/Ni-based coatings under different Ti:Nb ratios: a and b Ti:Nb = 6:1; c and d Ti:Nb = 3:1; e and f Ti:Nb = 1:1; g and h Ti:Nb = 1:3; i and g Ti:Nb = 1:6

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Fig. 5
Two graphs with fluctuating trends labeled a and b. F e (0.67, 4.80 k) and F e (0.67, 8.09 K) have the highest values in a and b, respectively. Each graph lists two columns for element and weight percentage.

EDS spot scanning results of Ti:Nb = 1:6 worn surface a region 1; b region 2

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Figure 6 is the surface morphology of the grinding ball after wear, there is a large block of adhesive on the surface of the grinding ball, mainly adhesion wear occurs. EDS analysis of the adhesive and grinding ball shows that the oxidation degree of the grinding ball surface is very low, and the distribution of elements on the surface of the grinding ball is similar to the worn surface of the coatings.

Fig. 6
A 4-part illustration labeled a to d. In a and b, have microscopic views of the surface morphology of the grinding ball with uneven texture and scattered particles. In c and d, two graphs plot fluctuating trends. F e (0.67, 7.40 k) and F e (0.67, 8.83 K) have the highest values in a and b, respectively.

Surface morphology and EDS results of grinding ball a Surface morphology of grinding ball under low magnification; b surface morphology of grinding ball under high magnification; c EDS point scan results for point 1; d EDS point scan results for point 2

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The wear debris morphology is shown in Fig. 7. The wear debris are mainly composed of large blocks, indicates that severe wear of the coatings occurred during the wear process. EDS analysis of the wear debris found that the main chemical composition of the wear debris is basically similar to the worn surface of the coatings and the worn surface of the grinding ball.

Fig. 7
A 2-part illustration labeled a and b. In a, it has a microscopic view of various irregularly shaped particles. In b, a graph plots a fluctuating trend. F e (0.67, 11.4 K) has the highest estimated value. It has a table with two columns and nine rows. The column headers are, element and weight percentage.

Wear debris and EDS results of coatings a morphology of wear debris; b EDS spot scan results of wear debris

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4 Conclusion

In this paper, the effects of different Ti:Nb ratios on the hardness, and wear resistance of Ni-based coatings are studied, and the results are as follows:

  1. (1)

    Compared to the substrate, the hardness of the coatings is improved.

  2. (2)

    The Ti: Nb = 1:6 coatings has the best wear resistance due to the content of Nb is much higher than that of other coatings.

  3. (3)

    The wear failure forms of the coatings are abrasive wear and slight adhesive wear.