GB2050434A

GB2050434A - Slidable members for internal combustion engines

Info

Publication number: GB2050434A
Application number: GB8015416A
Authority: GB
Original assignee: Nippon Piston Ring Co Ltd
Current assignee: Nippon Piston Ring Co Ltd
Priority date: 1979-05-10
Filing date: 1980-05-09
Publication date: 1981-01-07
Also published as: JPS55164070A; DE3017907A1; DE3017907C2; JPS585256B2

Abstract

A wear resistant slidable member for internal combustion engines includes a wear resistant flame sprayed layer on the sliding surface of the member comprising 20 to 97% by weight of a metal carbide having a Vickers hardness of at least 750, 0.5 to 4.5% weight of molybdenum, and the balance iron or ferro alloy. The wear resistant layer preferably has a porosity of not more than 30% and a thickness of not more than 2.5 mm.

Description

SPECIFICATION Slidable members for internal combustion engines The present invention relates to slidable members having highwear resistance for use in internal combustion engines, such as for example piston rings and cylinder liners.

Recently, there have been attempts to increase the compression ratio and rotation rate of internal combustion engines in orderto improve the operating characteristics of the engines. As a result, there is a requirement for the wear resistance of piston rings and cylinder liners to be improved.

Generally, wear characteristics can be classified into abrasion (grinding wear by foreign bodies having high hardness) and scuff, both of which phenomena have a great influence on the characteristics of an engine. Thus, it is impossible to obtain a satisfactory wear resistance without achieving adequate abrasion resistance and scuff resistance.

In order to improve wear resistance, it has been proposed to plate piston rings with chromium (hereafter referred to as "Cr-plated piston rings") and also to flame spray a layer of molybdenum on the sliding surfaces of piston rings (hereafter referred to as "Mo-flame sprayed piston rings").

However, it is very expensive to chromiúm-plate piston rings and also their scuff resistance is insufficient. Therefore, Cr-plated piston rings fail to meet recent requirements for the slidable members. On the other hand, Mo-flame sprayed piston rings are poor in abrasion resistance. In addition, molybdenum is an expensive element and hence cannot be used widely.

Thus, both Cr-plated piston rings and Mo-flame sprayed piston rings fail to provide the required combination of abrasion resistance and scuff resistance and hence have insufficient wear resistance.

Heretofore, it has also been proposed to flame spray slidabie members with molybdenum and a ferro alloy simultaneously to produce a porous layer comprising a ferro alloy phase, an alloy phase consisting of the ferro alloy and molybdenum, and a molybdenum phase. These known members contain a mixture of molybdenum and ferro alloy in order to improve the bond strength of the flame sprayed particles in the flame sprayed layer. In the mixed flame spraying of molybdenum and iron, however, the product has an insufficient wear resistance although it shows an improved bond strength between the flame sprayed particles in the flame sprayed layer.

It is, therefore, an object of the present invention to overcome or alleviate the above mentioned disadvantages of conventional slidable members.

Accordingly, the invention resides in a slidable member for internal combustion engines comprising a wear resistant flame spray layer on a sliding surface of said member, wherein said layer comprises, in final composition, 20 to 97% by weight of a metal carbide having a Vickers hardness of at least 750, 0.5 to 4.5% by weight of molybdenum, and the balance iron or a ferro alloy.

The metal carbide used in the flame sprayed layer should have a Vickers hardness (Hv) of at least 750 since satisfactory wear resistance required for slidable members for use in internal combustion members cannot be obtained with a hardness (Hv) of less than 750. The metal carbide having a hardness (Hv) of at least 750 contributes to the wear resistance and elevates the hardness of the whole flame sprayed layer. When the amount of the metal carbide is less than 20% by weight, satisfactory wear resistance and hardness cannot be obtained. On the other hand, with more than 97% by weight, wear of a complementary member which is in a sliding contact and in a relative motion with the slidable member becomes too great and scuffing tends to occur.

With regard to the molybdenum present in the flame sprayed layer of the invention, part of the element is in the form of an alloy with iron or a ferro alloy. If the amount of molybdenum is less than 0.5% by weight, the desired bonding between the flame sprayed particles by alloying of moiybdenum with iron or a ferro alloy cannot be obtained. This has an adverse affect both on the bond strength and the anti-stripping property of the wear resistant flame sprayed layer as a whole. When the molybdenum, content is increased above 4.5% by weight no substantial improvement of the anti-stripping property, which is ascribable to bonding between the particles by alloying of the molybdenum with iron or a ferro alloy, is observed.Thus, since molybdenum is an expensive material, it is advantageous from a cost viewpoint to limit the amount of molybdenum to not more than 4.5% by weight.

Porosity in the flame sprayed layer is important for retaining lubricating oils, but should be not more than 30%. This is because the strength of the layer is decreased and various problems such as dropping out of the particles and stripping of the flame sprayed layer tend to occur if the porosity is more than 30%.

The flame sprayed layer of the present invention exhibits excellent adhesion to the slidable member provided the thickness of the layer is not more than 2.5mm. It is, however, found that a flame sprayed layer of thickness more than 2.5 mm is susceptible to stripping.

Examples of the ferro alloy which can be used in the present invention include carbon alloy steel, and 16 chromium based stainless steel. Care must be taken in selecting the kind of ferro alloy to be used since the hardness of the whole flame sprayed layer is sometimes decreased depending on the kind of the ferro alloy used. Any ferro alloy that will not decrease the hardness of the whole flame sprayed layer can be used.

The wear resistant flame sprayed layer of the present invention can be obtained by plasma flame spraying a mixture of each powder of metal carbide, molybdenum, and iron or a ferro alloy on the slidable surface of slidable members. In this case, both a single metal carbide and a mixture of a plurality of metal carbides can be used as the metal carbide component. In addition, any two of the abovedescribed powders can be replaced by a powdered alloy of the two components or an alloy powder of ferro carbide containing molybdenum.

The present invention will be described in greater detail with reference to the following Examples, and the accompanying drawing which is a graph show ing the results of comparative wear tests performed on slidable members of the present invention and a conventional slidable member.

EXAMPLE Slidable member samples 1 to 3 were prepared from a conventional substrate having dimensions of 15 mm x 20 mm x 7 mm as follows: Sample 1 Molybdenum Powder 50% by weight Carbon Steel Powder 50% by weight (0.8 wtoiC) The above composition was flame sprayed onto the substrate to form a flame sprayed layer of thickness of 0.5 mm (porosity 15%; hardness on the Rockwell C scale of 40).

Sample 2 16 Chromium Stainless Steel 10% by weight Powder (16% Cr, 2% Ni, 0.2% C, balance Fe) Chromium Carbide Powder 87% by weight (13%C) Molybdenum Powder 3% by weight The above composition was flame sprayed onto the substrate to form a flame sprayed layer of thickness of 0.5 mm (porosity 5b/o). The composition on analysis of the resulting flame sprayed layer was as follows.

Metal Carbide (Hv 1,300) 83.7% by weight Molybdenum 3.1% by weight Ferro Alloy Balance Sample 3 Iron-Ferro Alloy Powder 97% by weight (3.5% C, balance Fe) Molybdenum Powder 3% by weight The above composition was flame sprayed on the slidable member to form a flame sprayed layer of a thickness of 0.5 mm (porosity 3b/c). The composition on analysis of the resulting flame sprayed layer was as follows.

Metal Carbide (Hv 950) 50% by weight Molybdenum 3% by weight Iron Balance These samples were fixed to a rotary wear testing machine and pressed on the upper surface of a disc material made of a steel (3.2% C, 2.0% Si, 0.8% Mn, balance Fe) having a hardness on the Rockwell C scale of 98 and the amount of wear was measured by rotating the disc material while supplying a lubricating oil onto the contact surfaces under the following conditions.

Test Conditions Amount of Lubrication Oil: 0.5 I/min Lubrication Oil: Daphne Oil # 65 Load: 20 kg/cm2 Abrasion Speed: 5 m/sec Driving Distance: 300 km The results obtained are shown in the drawing, from which it can be seen that Samples 2 and 3 of the present invention exhibited less than half the wear of Sample 1 which has the conventional flame sprayed layer of iron and molyb denum.

Claims

1. A wear resistant slidablememberfor internal combustion engines comprising a wear resistant flame sprayed layer on the sliding surface of said member, wherein said layer comprises, in final composition, 20 to 97% by weight of a metal carbide having a Vickers hardness of at least 750, 0.5 to 4.5% by weight of molybdenum, and the balance iron or a ferro alloy.

2. A member as claimed in Claim 1 wherein the porosity of said flame sprayed wear resistant layer is not more than 30%.

3. A member as claimed in Claim 1 or Claim 2, wherein said wear resistant flame sprayed layer has a thickness of not more than 2.5 mm.

4. A wear resistant slidable member as Claimed in Claim 1 substantially as hereinbefore described with reference to the Example.