Wear and coating of tillage tools: A review

Abstract

Tillage tools are the main soil engaging implements facing high abrasive wear. This paper provided an overview of the research findings published in the area of wear and coating of tillage tools. Many researchers across the world have studied on the wear behavior, coating materials and methods of the tillage implements. In the previous studies coating methods and materials were used to resist the tillage tools against the wear phenomena. The effect of soil type on the wear of parts of impalements is investigated and reported in various research works. Draft force of the coated of the parts of tillage implements have also been measured and compared against the uncoated ones and presented in various publications. Many other scientists have considered and worked on the modelling of the wear of tillage tools. Several parameters such as tool geometry, soil properties including moisture content and soil texture and performance parameters of tillage tools such as forward speed and depth have been noticed in the wear modelling. The reviewed studies indicated that the wear rate of tillage implements increases with the increase of the size of sand particles in the soil. The previous investigations showed the less consumption of draft force by the coated tillage tools. This review helps those who are interested in work on the wear behavior aspects of the soil engaging implements and the coating of soil tillage tools.

1. Introduction

Food security depends mainly on the agriculture section in the world. Production of agricultural crops needs mechanized operations. Land preparation (soil tillage), crop planting, crop protection, harvesting and post harvesting stages are needed in agricultural mechanization. Among these operations, tillage is the most important operation in the production of agricultural crops. Tillage is the procedure which needs high draft force to pull the implements, i.e., moldboard plow, disc, chisel plow, rotivator, and sweep blades, in the soil (Fig. 1). The proper soil preparation leads to achieve more crop yield. This needs to have durable tools facing the soil with different texture especially hard soils. Therefore, the materials used in tillage tools require strength to resist impact and hardness to resist wear in agricultural farms [38]. Much interest in increasing tillage tools lifetime by increasing the wear resistance have been noticed by many researchers. Previous studies have shown that the wear of soil engaging farm machinery can be reduced by composite coating [29], alumina ceramic coating [19], hard facing [7]: [24,27,63,64,80,81], plasma restoration and hardening [37], carbo-vibro-arc hardening [34] and hot stamping [17,80,81].

Fig. 1.

Different types of tillage tools.

The surface degradation of metal is a result of wear phenomena that indicates material loss due to motion between metal surface and other materials. The wear of material depends on the properties of its surface such as roughness and hardness [39]. The abrasive wear in tillage tools is the most common problem. The high wear rate of soil engaging tools leads to loss of material, recurring labor, downtime and replacement costs of worn out parts [7,39,70]. The wear of tillage tools is one of the problems in the process of agricultural crop production which should be taken into consideration. In this case, coating techniques such as arc-PVD and plasma spray methods can be employed to increase resistance to wear of tillage tools surfaces. Sweep duck blades are among those tillage tools which is commonly used in soil preparation. Researchers have shown interest on titanium-based materials due to their low friction coefficient, high thermal stability, and resistance to oxidation and wear [77,79]. Titanium (Ti), Titanium Nitride (TiN) and Titanium–Aluminum–Silicon-Carbo Nitride (TiAlSiCN) are among the titanium-based composites. Their characteristics have made them a perfect compound to be utilized in many coating industries, for instance, cutting tools [71], dies and molds [75], turbine and aircraft compressor blades [26,72], ploughshares and other tillage tools [46,60]. Besides TiN, other materials such as, TiAlSi [45], TiAlN [10], and AlSi [73] have been successfully deposited by arc-PVD method for tribological investigations through which, gaining proper crystalline quality has been proven. The metal elements which is distributed into the soil during the operation of soil tillage is investigated in a recent study. The researchers of this study introduced numerous chemical elements remaining in the soil from wear behavior of tillage tools including Al, B, C, Co, Cr, Cu, Fe, Mo, Nb, Ni, P, Pb, S, Si, Ti, V, W and Zr. They also reported that these elements may cause a toxicological threat [35].

Wear of agricultural machinery parts will effect on the cost of agricultural operations. The replacement of worn parts of the tillage tools affects in the time of land preparation. It will delay the time of tillage and crop planting. This would then influences the productivity of the crop production. It is, therefore, important to take into consideration the economic aspects of the wear of tools in the farm. In an investigation the cost involving the wear of agricultural tools is reported significantly high. It stated that the total annual losses because of the wear is approximately $940 million in year according to Natural Research Council of Canada [38,70]. It also reports that in Australia, farmers expends more than 40 million dollars for a year for buying and replacement of sweep duck blades [70]. For many years researchers have attempted to decrease the cost of tillage practices by applying wear resisted coating material on the tool surfaces [1,7,8,9,13,17,23,27,34,37,39,43,44,46,80,81,85]. They were trying to find a suitable way to protect the surface of tillage tools. In this regard, some tillage tools such as moldboard plow [8,27,43,46,80,81], sweep blades [13,57,58,85], rotivator blades [23,44], and chisel tines [7] have been coated by different coating materials. Some other researchers coated a piece of steel (CK45 and CK60) or electrodes made of steel 12 014.20 to study the weight loss of the steel [36]. The coating of tillage machinery surfaces improves the life of the worn parts of the machines and decreases the replacement cost. The objective of surface coating technology is to deliver wear resistance surfaces. Various types of coating materials can improve the wear resistance of materials. Physical vapor deposition (PVD), chemical vapor deposition (CVD), chemical and electrochemical plating, plasma spraying and thermal spraying are the different coating methods which will be explained as follows. The wear in agriculture tillage tools is prevalent and there are some review papers on this subject. But it feels that more reviews are needed in order to better understand the wear and the coating methods of the tillage tools for scientists and researchers working in this field. A review of wear of tillage tools was carried out by Ref. [83] that explained constraints in transferring the research findings in the wear of tillage tools to agricultural sector.

2. Surface coating methods

2.1. Physical vapor deposition

Physical vapor deposition (PVD) technology includes different techniques namely; evaporation, sputtering, ion plating and ablation. PVD method can be used for deposition of both thin and thick films. The PVD methods rely on coating deposited on a substrate with given composition. Solid material may be deposited onto any solid material. Polymers are exception of this deposition [14]. The PVD method has been used in many research works to coat different materials, especially titanium-based materials on tillage tools (Table 1). In this method, coating thickness could be differed from 4 to 6000 μm depending on coating technique and coating materials.

Table 1.

Coating methods, materials and thickness used in tillage tools.

Coating methods	Technique	Coating materials	Coating thickness (μm)	Tillage tool	Reference
PVD	Arc	TiN TiN TiCrN–TiAlN–TiAlSiN–TiAlSiCN	4 4 4.2	Ploughshare Sweep blades Sweep blades	[50] [57] [58]
	DC-magnetron Sputtering technique	CrN	6000	Reversible Cultivator Shovels	[13]
	Laser	Al-1236 powder	2000	Sweep blade	[85]
	Multi-arc ion plating	TiAlN CrN	20	Rotary tillage blades	[23]
–	–	Teflon	– Thin sheet	Rectangular slider Simple tillage tools	[41] [20]
–	–	Polysiloxane/T8 composite Composite	– –	Bulldozing blades Chisel tine	[29] [52]
–	–	Thermoplastic(SiO2, Al2O3, Iron Copper and glass fiber as filing material to Polyamide(PA6) and Polyethylene (PE))	1000	Low-carbon steel	[1] [2]
Electrochemical method	Electrolysis	Hard chrome	25	Ploughshare	[50]
Chemical process	Decreasing chemical application	Electroless nickel	20	Ploughshare	[50]
Electro sparkling	–	High speed steel Alloy of iron Alloy of cobalt and carbides of Titanium and tungsten	5–200	Cultivator sweeps	[69]
	–	D517 coatings		Furrow opener (Q235 steel)	[78]
	–	White unalloyed cast iron	100	–	[55]
CVD	–	SiC	1–50	–	[42]
- Hardfacing-Weld overlay-Weld cladding	–	Covered electrode and welding wire	–	Moldboard plow	[63,64]
			–	Ploughshare	[16] [7] [27] [24] [80,81]
Thermal spray	Plasma spray	Nickel based alloyed powder	–	Cultivator sweeps	[38]
	Plasma spray High velocity oxy-fuel(HVOF) Arc spraying	Al2O3–TiO2/NiAl WC-Co NiAl	350 350 50–80	Rotary tiller blades	[31]
	Thermal spray	WC-Co-Cr Cr3C2NiCr Stellite-21	100–150	Rotavator Blades	[30]
	Plasma spray	Poly tetra fluoroethylene (PTFE)	20	Rotary tillage blades	[23]
	Electroless composite plating	Ni–P-PTFE	20	Rotary tillage blades	[23]
	Plasma nitriding	Nitride	–	Small dimension of carbon steel CK45 used in farm equipment	[54]
	Plasma spray	Ferrous Alloys Non Ferrous Alloys Carbides Ceramics	400–2500 50–500 150–800 100–200	–	[42]
	High Velocity Oxy-Fuel Flame (HVOF)	25% (Cr3C2-25(Ni20Cr)) + NiCrAlY Ferrous Alloys Non Ferrous Alloys Self-Fluxing Alloys Carbides Ceramics	– 50–2500 50–2500 50–2500 50–5000 250–2000	–	[74] [28] [42]
	Electric arc surfacing	Ferrous Alloys Non Ferrous Alloys Unalloyed cast iron	100–2500 100–2500 100–5000	– –	[42] [55]
	Electro deposition	Nanocoatings(Hydrophobic + ceramic coating spray) Nichel chrom plating	200 multilayer	Chisel blade	[18]
Thermal diffuse	Carbonitriding	carbonitride	140–470	Ploughshares	[63,64]
	Carburizing	Carbon	–	Tillage blades Cultivating machines Ploughshare	[48] [51] [80,81]
	Boronizing	Boron	–	Tillage tools	[82]

2.2. Chemical vapor deposition

Chemical vapor deposition (CVD) forms a thin solid film on a substrate material with a vapor produced by chemical reaction [74]. CVD is a non-line-of-sight process with a good throwing power. Therefore, the components with complicated shape can be coated by this method. It can also deposit films with good coverage [59]. The thickness in CVD is usually used for coating is in the range of 1 to 50 μm (Table 1).

2.3. Electrochemical deposition

Electrochemical deposition, or electroplating, is a method for depositing metals as layers onto selected conductive substrates. Electrical current is used for the deposition process. In electrodeposition, available ions in the electrolyte or from the anode, through a replenishment process, deposit on the negatively charged cathode, carrying a fixed amount of charge measured as current in an external circuit. Achieving the perfect particle size in the nanometer range during the electrodeposition process requires modification of variables such as bath composition, pH, temperature and current density [3]. In electroplating, the cathode is the electrode coated by electroplating. Metals such as aluminum and titanium are excluded from this method. Brush plating uses hand plating tools instead of baths. The anode in the electrolyte is a material for anodizing aluminum and its alloys, producing an oxide layer on the surface [74]. [53] described electrochemical deposition as a method that allows thin desired metal coatings to be obtained on the surface of another metal by simple electrolysis of a watery solution containing the desired metal ions or their complexes. In fact it is a technique of obtaining a desired coating by chemically reducing the metal ion or its complex on to the substrate in a controlled method.

2.4. Plasma spraying

Hot thermal plasma torch or spraying is a method used to deposit nano or micro powders of metals or ceramics on to metal alloy substrate. The high temperature plasma formed at the tip of the plasma torch ionizes the powders inserted at the front of the troch. The ionized powders through hot plasma of different gasses meet the surface of metals substrates and form thin films. These thin films are either metal or compounds due to reactions with gasses used. For example, Ti powders are deposited with nitrogen plasma leading to the formation of TiN thin films and with oxygen plasma to form TiO2 [33]. The size of the sprayed particles is typically 10–100 μm. The minimum layer thickness to form a uniform layer is approximately 50 μm [74]). Thus plasma spray method can coat metals with a non-reactive deposition using Ar and reactive deposition using reactive gasses. A schematic of plasma spray principle is shown in Fig. 2 [42].

Fig. 2.

A schematic of plasma spray principle [42].

2.5. Thermal spraying

Thermal spray is used for a group of coating processes to apply metallic and nonmetallic coatings. Plasma arc spray, flame spray and electric arc spray are the processes. The processes of thermal spray are using in different sectors such as automotive engines, gas turbine, medical, mining, food processing and agriculture. The advantages of thermal spray are a) the use of wide variety of materials for coatings, b) the ability for applying coatings to substrate without significant heat input and c) the ability to strip off and recoat worn or damaged coatings without any change of part properties or dimensions. Of course, there are some limitations as the thermal spray process can only coat what the torch or gun sees. They also cannot coat small and deep cavities into which torch will not fit [14]. In the other definition by Ref. [25] thermal spraying involves a variety of seemingly simple surface processes in which solid materials (wires, rods, and particles) are rapidly heated by a plasma jet or combustion flame, melted, and propelled against the substrate to be coated.

3. Coating methods and materials used in tillage tools

Table 1 presents a review of differences on the coating methods, materials and thicknesses used for soil-tool engaging coating. A variety of soil engaging implements have been coated using different materials with different thicknesses in the previous worldwide researches. The various coating techniques in each method were applied for coating of parts of implements. The PVD method have been applied for coating of tillage tolls such as ploughshare [50], sweep blades [57,58,85], reversible cultivator shovels [13] and rotary tillage blade [23]. Ti based coating materials have been used in the PVD method. Electro-chemical and chemical process have been used for coating of ploughshare by hard chrome and electroless nickel [50]. Cultivator sweeps and furrow opener were coated by the electro sparkling method [69,78]. According to literature review no reference was found for CVD method for coating of tillage tools. Some materials such as Teflon, polysiloxane, composite and thermoplastics have been reported to be used for coating of respectively, rectangular slider [41], simple tillage tools [20], Bulldozing blades [29], chisel tine [52] and low carbon steel pieces [1,2]. Hardfacing-Weld overlay-Weld cladding method has been used for coating moldboard plow by electrode and welding wires [16,63,64]: [24,27,63,64,80,81]. There are a wide range of applying thermal spray techniques for coating of cultivator sweeps [38], rotary tiller blades [31], rotivator blades [30], rotary tillage blades [23], small piece of CK45 used in agricultural machinery [54] and chisel blade [18].

4. Wear of tillage tools and soil type

The soil properties and its impact on any study of soil and machine relationship are taking into account by researchers and experts. The properties of soil can influence on the wear rate of the different tools engaging with soil such as ploughshare, rotary tiller blades, sweep blades, chisel tines, disks. One the soil properties is the type of soil. The most common problem of the tillage tools is the deterioration caused by coarse particles in soil. The abrasive wear of tillage machines usually caused by soil particles results in the higher fuel consumption, loss of energy which leads to increase repair and maintenance costs. It also affects on the quality of tillage operation. In this regard, some investigations have been conducted on the assessment of wear rate on various soil types (Table 2). The results of those studies indicated that the wear rate of tillage implements increases with the increase of the size of sand particles in the soil. The surface roughness of the tools is also affected by the type of soil.

Table 2.

Wear and soil type.

Soil type	Remarks	Reference
Sandy clay loam	The wear of tested materials increases with an increase in the forward speed. The dependence of wear strength on forward speed for each material can be expressed by an equation in the form of a square polynomial.	[76]
Clay Loam Sand	A strong correlation was found between soil type and moldboard plow share wear for different hardness values of the share	[47]
Clay Loam Sand	The wear rate of sandy soils is higher than that of loamy and clay soils. It also depends on the stone content and its size.	[62]
Fine sandy loam Sandy loam/Loam	The surface roughness of the ploughshares with an increased proportion of coarse particles was higher than that of the ploughshares with a higher proportion of fines.	[68]
Clay loam	The effective wear rate of the rotary tiller and rotary harrow tool was similar to and higher than that of the small power rotary tiller, which showed the best wear resistance in field tests.	[21]
Sandy loam Clay	The wear of shears working on sandy loam soil was about 37% greater than on loam soil.	[49]

5. Coating material and draft force of tillage tools

Tillage operation in agriculture consumes the considerable amount of energy to manipulate the soil at the desired depth. The components that engage with the soil are facing much more abrasive wear. The friction induced by the wear causes much more force to pull the tillage tools. Therefore, coating of the surface of the parts engaged with the soil can reduce the soil-tool friction and consequently the wear. This leads to consume less draft force by the implement. Some experiments have been carried out on the subject of the effect of coating material on draft force of the tillage tools by some researchers (Table 3). The results of these investigations showed the less consumption of draft force by the coated tillage tools including moldboard share, chisel tine and sweep blades compared with uncoated ones.

Table 3.

Effect of coating materials on draft force.

Coating materials	Tillage tool	Remarks	Reference
Carbon nanotube-hard chromium composite	A simple tine	The draft requirements of the coated carbon nanotube hard chromium composite tillage tools were approximately 43.92%, 44.14%, and 38.02% less than the uncoated tools, respectively.	[84]
Teflon and Chromium	Moldboard share	A minimum draft of 0.235 kN was achieved with a Teflon-coated moldboard at a forward speed of 2 kmh-1 and a humidity range of 20–25%. A maximum draft of 0.336 kN was achieved with an uncoated plow bottom operating at a speed of 4 kmh-1 in a moisture range of 30–35%.	[40]
Ultra high molecular weight polyethylene (UHMW-PE)	Chisel tine	It has been found that the modification to the furrower tines by UHMW-PE coating can reduce draft force significantly.	[5]
TiCrN–TiAlN–TiAlSiN–TiAlSiCN	Sweep blade	The draft force of all blades showed promising results. As the travel distance increases the draft force decreases for multilayers coated blades compared with uncoated.	[58]
Laser coated sweep	Sweep blade	A significant decrease in draft force of all sweep blades was found after 74 km of operation.	[85]
Nickel based alloyed powder	Cultivator sweep blade	After 74 km of operation, a significant drop in draft force was reported for all sweep blades.	[38]

6. Wear of tillage tools and modelling

Some attempts were made to model the wear mechanism of soil engaging implements. Table 4 shows a review of the studied related wear modelling. The factors which have been considered to model soil-tool wear behavior are soil and tool parameters. The soil properties such as soil texture and soil moisture content are the most common used properties in the studies of the wear modelling of tillage tools. The working depth and forward speed of the tillage equipment are the other factors that have been used for modelling. The contact pressure between the soil and tool is the other parameter. Different methods such as finite element method (FEM), discrete element method (DEM), mathematical and numerical methods have also been used to model the wear of tillage tools. DEM and FEM are the main methods that are considered for the soil and tool interaction studies.

Table 4.

Wear modelling of tillage tools.

Wear factors	Modelling method	Soil engaging tool	Reference
Soil load, Soil stress, Tine geometry	Discrete element method (DEM)	Steel specimens used for tillage tools	[56]
Roughness & hardness of the tool surface, Mechanical properties of the tool material, Tool geometry, Soil density, Working speed	Theoretical & Mathematical	hisel blade	[11]
Density, Young's modulus, Poison ratio, Angle of friction, Flow stress ratio, Dilation angle, Initial yield stress	Finite element method (FEM)	Tillage tool Cultivator tip Cultivator tip	[65] [66] [67]
Chemical composition of steel, Soil type, degree of soil compaction, Working depth of tool, Distance travelled, Position of the wearing part of tool	Mathematical	Wedge-shaped blade	[49]
Applied load, Relative speed, Material hardness, Contact pressure of soil and tool, Slip	DEM	Tillage tool	[4]
Soil properties, coefficients of restitution, Poisson's ratio, shear modulus, and the particle density of soil.	DEM	Steel bar	[22]
Metal: Young modulus, Poisson ratio, and Power strain hardening law, Soil: Ploughing force, Tangential force, friction coefficient,	Numerical study by FEM	Specimens of a bar of AISI316L	[6]
Working days, Working depth of tool, Studied area	–	Chisel blade	[15]
Normal force, Surface fatigue, Number of convolutional layers, Filter size, Kernel size, learning rate	Artificial intelligence	–	[61]
Hardness, Force, Velocity, Friction coefficient of soil particles between itself, Young modulus, Strain	Mathematical, DEM, FEM	Chisel blade	[12]
Soil mechanical properties, Tine geometry, Load, Sliding distance, Hardness	Numerical simulation of chisel tine motion in the soil by DEM	Chisel tine	[32]
Soil pressure to working surface, hardness of deposited coating, friction path, hardness of main metal, volumetric weight of hard weld alloy, volumetric weight of main material, duration of working of the part in the soil, forward speed, soil hardness, specific weight of main material	Mathematical model	Hard-faced ploughshare	[16]

7. Challenges

Although there have been conducted many studies of the wear and coating of the tillage tools, but the lack and/or limitation of information on different aspects of the wear of soil working implements is still sensible and needs further research. Thus the challenges in the form of some questions remains about this issue. What is the appropriate life time of a tillage tool which could work properly in an agricultural field? What are the costs of replacement of parts of tillage machines in order to get the high efficiency of the machine performance? What percentage of the agricultural production costs does belong to wear of tillage machinery? What are the effects of dimensions (in regard to narrow and wide tines) of parts of the tillage tools on the wear? Different climates conditions will probably affect the wear behavior of parts of tillage machinery. In that case, what kind of climate conditions is suitable for reduction of wear of tillage tools? How and what is mechanisms between coating techniques and wear of soil tillage tools?

8. Conclusion

Wear is a major problem in agricultural implements especially in soil tillage tools. This paper sums up the research works on the subject of wear of tillage tools and different methods which is applying for coating of tillage tools. The properties of soil can influence on the wear rate of the different tools engaging with soil such as ploughshare, rotary tiller blades, sweep blades, chisel tines, disks. The reviewed studies indicated that the wear rate of tillage implements increases with the increase of the size of sand particles in the soil. The investigation of the impact of coating material on the draft force showed the less consumption of draft force by the coated tillage tools including moldboard share, chisel tine and sweep blades compared with uncoated tools. The efforts which have been made to model the wear mechanism of soil engaging implements are also presented in this review. Several factors which have been applied in the wear modelling are tool geometry, soil properties (moisture content and soil texture, coefficient friction of soil), metal properties (Young modulus, Poisson ratio, strain and hardness) and performance parameters of tillage tools such as forward speed and depth. Wear of agricultural machinery parts will have an effect on the cost of agricultural operations. It also influence on the productivity of the crop production. Therefore, it is important to take into consideration and assess the economic aspects of the wear of tillage tools in the farm. There will be remained some questions about the appropriate life time, the desired working depth and manufacturing process of tillage tools, and the influence of suitable climate conditions on the wear rate of tillage tools which needs to be tackled by further investigations. This paper has tried to review the articles in the subject of wear and coating of tillage tools published in the high ranking world scientific journals. It could be applicable for the researchers who are interested to work on this area.

Author contribution statement

All authors listed have significantly contributed to the development and the writing of this article.

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No data was used for the research described in the article.

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Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.