RU1782996C - Method for applying multilayer ionic-plasma antifriction coating to piston rings - Google Patents

Abstract

Usage: in the field of hardening of machine parts, namely when applying antifriction layers to the surface of piston rings of internal combustion engines by ion-plasma deposition. The inventive method for applying a multilayer ion-plasma anti-friction coating on rings, which consists in preliminary determining the optimal thickness of the running-in and intermediate layers, followed by applying the running-in, wear-resistant and intermediate layers on the piston rings, during the coating process, the thickness of the wear-resistant layers is controlled, based on the condition given in the claims. 4 ill.

Description

with

with

The invention relates to the field of hardening of machine parts, and in particular to methods for applying antifriction layers to the surface of piston rings of internal combustion engines (ICE) by ion-plasma deposition.

A known method of applying hardening coatings to piston rings of internal combustion engines, which includes the formation of wear-resistant ceramic and running-in metal layers to reduce cylinder wear at the running-in stage, and increasing the service life of the piston rings.

The disadvantage of this method is that it does not provide the required adhesion of the coating to the surface of the ring. In addition, there is a limitation on the thickness (5-7 μm) of the ceramic wear-resistant layer

because of the danger of developing through cracks in it and the subsequent destruction of the coating under the action of mechanical and thermal stresses during operation of the engine.

There is also known a prototype method for applying a multilayer coating with variable properties and chemical composition, which consists in applying a sublayer that binds the coating and the part and wear-resistant layers alternating with intermediate layers, with a preliminary choice of the optimal coating thickness selected by two parameters: the average resistance of the part and the coefficient of variation. As a rule, the region of optimal values lies between the minimum values of the variation of resistance - and the maximum average resistance.

Xi 00

ND

However, from the point of view of the stability of the multilayer coating, the correct choice of the thicknesses of its layers is necessary. Too thin layers wear out quickly and do not give the desired effect, thick layers tend to break under the action of stresses arising in the coating. This is especially true for ceramic layers due to their low ductility and tendency to crack, which increases the likelihood of a dangerous defect that can lead to dynamic destruction of the coating.

The aim of the present invention is to reduce the wear of the cylinder-piston ICE pair by eliminating uneven wear of individual sections.

This goal is achieved by the fact that in the method of applying a multilayer ion-plasma anti-friction coating to rings, which consists in preliminary determining the optimal thickness of the running-in and intermediate layers, followed by applying the running-in, wear-resistant and intermediate layers to the piston rings, the thickness of the wear-resistant is controlled during the coating process layers based on the condition

P | sd (0.7-0.8),

Where

, yy / 2

 T i fOA GL / a

) yG-f; (

AtaD1 ™

 CЈ

 WITH; C; f7) f C,

ЈЈ -4rWA4- - "/

 fJttW- g. w.f, V / 4№

where hi is the controlled layer thickness; 50

H b - a, a is the inner radius of the ring;

b is the outer radius of the ring; The central angle in the lock of the ring in the open state;

n is the total number of layers; 55

yi is the work of adhesion at the boundaries of the layers;

Ei, i, Eo, are the elastic modulus and Punch coefficient for the materials of the layer and ring, respectively;

0

5

0 5

0

5

0

5

0

5

a - coefficient of thermal expansion of the ring:

T (Z) is the temperature distribution over the thickness of the ring;

P, YI, p, mp - take into account the thickness of the layer hi and the elastic characteristics of the layer and ring;

tj, d - take into account the layer thickness and thermal expansion coefficients of the layer and ring;

ci (Z) is the concentration of atoms embedded in the interstitial;

Rni is the radius of the pore in the lattice of the layer;

Rnp is the radius of the implanted atom.

The proposed method for applying a multilayer ion-plasma anti-friction coating to piston rings is as follows.

The optimal thicknesses of the running-in layer and the intermediate layers are preliminarily determined based on the specific conditions of manufacture and use of the piston rings. Then, an intermediate adhesive sublayer is created on the previously cleaned working surface of the piston ring by introducing metal atoms (for example, Ti, Zr, Hf, Cr, Mo) with icon implantation to a depth of 500-1000 A with a gradual decrease in the ion mean free path and the transition from implantation to the deposition of metal atoms on the surface of the ring. A first ceramic wear layer is applied (e.g., TIN, ZrIM, HfN, CrN). During the deposition process, the thickness of the wear resistant layers is controlled. To control the thickness, we use the calculation of the stress state of the ring with a multilayer coating and an assessment of the resistance of the coating to shear forces at the boundary of the layers at the most likely place of occurrence and development of cracks according to the condition

  (0.7-0.8) PiKp, (1)

where P | sd - shear forces acting on the boundary of the layers; P | kr is the critical shear force at which the growth of the boundary crack begins; A 0.7-0.8 coefficient corresponding to the safety factor adopted for such products (3). To determine the thickness of the wear-resistant layer meeting condition (1), we consider a coating consisting of and layers, each with a thickness hi, deposited on a substrate with a thickness H (Fig. 1). H b - a, where b is the outer radius of the ring, and a is the inner radius of the ring. The coating satisfies the condition

2 hi «N. Let us take the plane stress i 1

state with nonzero components of the stress tensor ck -.

Elastic constant bases and coating layers will be considered known.

Let stresses Oj (Z) exist in each coating layer under the influence of technological and operational factors. Shear forces acting on the boundary of the 1st layer with 1-1 layer

n Z | + h |

) / 0i (Z) dZ, t Zi

(2)

where Z | is the moving coordinate corresponding to the lower boundary of the layer.

Assume that a through fracture has occurred in the coating (at x -1 -, Z ZJ), and at the interface between the layers at x there is a semi-infinite crack of technological or operational origin.

Limit values of deformation at which the crack moves and peeling of the coating occurs (4)

r2yi (1-Ai / 2

ЈKR (, with hi EI

(3)

where y | - adhesion work, which is the energy cost of increasing the unit area of a slip crack; h, / L, thickness, Punch coefficient, and Young's modulus of coating at, respectively. For multi-layer coating

hi y hi;

(4.1)

 - E |

(4.2)

2 (MI: hi)

hf (Ei; hi)

 (4-3)

where hi. j, EI - correspond to a separate 1st layer.

Since, the underlying layers and the substrate can be represented in the form of an infinite half-space, and the coating in the form of a strip. From compatibility condition 4

G-

(5)

Substituted (5) in (3)

(6)

rfP o (-JAll y / 2

 V (

The transition to linear efforts m using Rkr ofp hf, we get

-pfP (2)) i / 2

1-tf

(7)

twenty

where Pcr is the critical force at which crack growth and peeling of the coating occur. Expression (7) is valid for both tensile and compressive forces.

5 From (1), (2), (3), (7) it follows that for the estimation

In order to work, it is necessary to know the dependence o; (Z) for each layer. The value of o; (Z) is the sum for ion-plasma coatings on three-piston rings

10 components

oj (Z) of (Z) + of H (Z) + of (Z), (8) where of (Z) are temperature stresses,

of (Z) - internal stresses caused by the introduction of 15 bombarding ions,

of (Z) - operational voltages.

The temperature stresses in the 1st coating layer are caused by the difference in the thermal expansion coefficients a (ctr) of the materials of the layer and the substrate. Since hi H, then

contribution to of (Z) from the difference 1st layer

and other coating layers can be neglected.

Given the linear dependence of E and a on

25 temperatures for a layer of thickness hi at

T f (Z) 5

tf (2} - And (Z) (Z) (Z)

 (z) -, TCZ)

30 x dt (Z), (9)

where To is the temperature after precipitation (operating temperature) aiaoci

yi a0cibi + aicibi + fiaia0 fiaobi + fiaibo + bobici

fy fibibo

rji (1 - p) Ha0 + (1 -fio) hiai 5 | (1- / l) Hb0 + (1 -fio) hibi ai; bi; ci; fi - coefficients in the form of 40 x

Ei ai + biT (Z) Eo ai + b0T (Z) Acn Gl-Qb ci + biT (Z) The indices I and о correspond to the lth layer and 5 substrate.

Internal stresses during ion-plasma deposition are caused by the incorporation of accelerated ions into the substrate and into the coating. The introduction of impurities into 50 volumes of a unit cell leads to a distortion of the crystal lattice and the appearance of stresses in the vicinity of defects. In the case of insertion into the interstitial, the magnitude of the distortion of the crystal lattice 55 is determined by the ratio of the radii of the impurity atom and the pore into which it is introduced. In the field of elastic deformations at low concentrations of interstitial impurities (less than 0.81 at.%

Be- N

W,. ,, .. A - ..,. ., city, 35

f, aChn ° GMJ ° - - -. fcf "-.) cg)

B where M and N are determined from the expressions (13)

where-IP4) 2L40 Consider a piston ring with a multi-a - A a b (In-g-) 2-layer coating. Using the condition of non-71-2h deformability of deformations and neglect

2 (0 - a) by the influence of the coating on the distribution on N (b2 - a2) 2 - 4a2b20n -) 2. (14) the stresses in the RING array can be considered

A45 that the operating voltage in the i-th

The radial stresses on the surface of the coating are determined by deformations when g and r b are equal to zero. The entire array of the ring, taking into account elastic

Tangential stresses of maximal properties of constant sparks. those. small on the surface and equal fr

 - (2a2 p- | n-b2-a2) 05) 50 C, ()

Temperature stress in piston - p (e -arf) /./hz z

the ring appear due to the uneven - oKlT (g) - - - f-f-KiClu4v-Q - & - a1}

its heating during engine operation. °

Radial and tangential stresses, 55 (3)

arising from heating rings,

calculated by formulas (6)., E

 i r if1 D -

.t “f fllnrJr ltfi.ju, 1 (16)% -J.tfiJrMrilr M,

-c.v.iЈ.) --b-ir, .rsf., i.j Substituting formulas (9), (10), (23) into the expression fa ° f (item (8) we obtain the general dependence for

determining stresses in the i-th coating layer on the piston ring.

, M.Hpv, ™ .W

N I; -DPR LeI, Eo fj

E; C; (g) -jz C e.Ttfj ..- fof-.eV ()

Using expression (24) in conjunction with formulas (1) and (7). control the thickness of the wear-resistant ceramic layers, at which shear forces at the boundaries of the layers are less than critical by 20-30%. or Rsd (0.7-0.8) Rkr. which is the optimal ratio for controlling the thickness of the coating layers and provides the maximum possible thickness of the wear-resistant layer while preventing the development of cracks in it (see Table 1).

The ratios Rsd and Rkrusiliy, at which the development of cracks in the coating does not occur, were determined experimentally by not loading the coated ring and simultaneously monitoring the appearance of cracks in its surface layer.

As can be seen from the above table. 1, at 9Pcr, no damage to the coating is observed.

At the same time, with a decrease in the minimum acceptable value (optimum), the Sd decreases and the thickness of the wear-resistant coating layer in accordance with expression (7), which leads to a decrease in the total life of the ring (Fig. 3).

After that, an intermediate metal layer is applied, then a second wear-resistant layer with a thickness controlled similarly to the first, and a second metal intermediate layer. The formation of an antifriction coating is completed by applying a run-in metal layer.

Example. Coatings consisting of TIN and Tf layers were applied to the piston rings of a two-stroke engine of the Tula motor scooter in a Bulat-type installation. The material of the rings was special cast iron with a% composition: Total 3,6-ZD; Sow 0.55-0.8; Si 2.5-2.9; MP O.Y-0.7; P 0.3-0.7; S 0.07; Cr 0.12-0.25; NI 0.6-0.15; Mo 0.15-0.35; Ti up to 0.1; Si traces; the rest is Fe.

The diametrical error of the piston ring after grinding of the working surface is ± 5 microns. To eliminate this error and to prevent ring wear on individual spots, it is sufficient to apply an upper running-in layer of 3 microns thick.

During the operation of the ring, the metal of the intermediate layer 5 is distributed along the walls of the cylinder. The thickness of the intermediate layer should be as minimal as possible. it is wearing and does not directly contribute to the duration of the coating. At the same time, as experimental studies have shown, its thickness cannot be less than 1 micron to reduce shear forces at the boundaries of the layers. Therefore, the optimum5 for the thickness of the intermediate metal layer is 1-1.5 microns.

An adhesive sublayer was created by accelerating titanium ions, T in the direction of the surface of the rings with a gradual decrease in the negative bias potential on them from 1700 to 100 V for 5 min. The wear-resistant TIN layer was deposited under the deposition conditions shown in the table. 2.

5 During the deposition of a wear-resistant layer, its thickness was controlled by the expressions (1), (7), (24) to prevent peeling of the coating as a result of crack growth. The results of calculating the stress distribution over the coating layers are shown in Fig. 2a. The hatched region represents the contribution from the process stresses arising from the coating deposition process. As a result

In 5 calculations, the optimum thickness of the wear-resistant layer was 3 μm. The forces at the boundaries of the layers with the obtained distribution 0j (Z) and the thickness of the wear-resistant layers are shown in Fig.2b. They are significantly

It is less than the critical shear stress leading to the growth of the boundary crack and the destruction of the coating.

Then an intermediate metal layer of titanium was deposited with a dense structure 1 μm thick (see Table 2}, after which a second wear-resistant layer was applied in composition and thickness similar to the first. At the end, a running-in layer of titanium 3 μm thick was deposited (see table. 2)

0 The total thickness of the wear-resistant layer was 6 microns. The microhardness of the wear-resistant layers at a load of 100 g was 2400 kg / mm2, the intermediate layers were 600 kg / mm2, and the running-in layer was 700 kg / mm2.

5 Experimental methods of the claimed method for applying a multilayer ion-plasma anti-friction coating to piston rings have been shown to be stable and durable, and showed that

Compared with the method described in the prototype, the claimed method provides a reduction in cylinder wear by 30% and an increase in the service life of the rings by a factor of three. In addition, the wear of the working surface of the cylinders is uniform, the same was observed on the surface of the rings after a half-hour running-in (Fig. 3).

Claims (1)

The claims A method of applying a multilayer ion-plasma anti-friction coating to piston rings, including preliminary determination of the optimal thickness of the running-in and intermediate layers and the subsequent application of running-in, wear-resistant and intermediate layers on the rings, characterized in that, in order to reduce the wear of the cylinder-piston pair by eliminating the uneven wear of individual sections, the thickness of the wear-resistant layers is controlled during the coating process, based on the condition P | s - (0.7-0.8) P | kr, where P | sd - shear forces acting on the boundary of the layers; P | kr is the critical shear force at which the boundary crack growth begins 4 -Јfcfow, 4TaЈ9 -f J I -. At ft 4 (h) EG -1 ph; ) / fr / Tfl) G; h) -nJ ft) Y.) viTib) 4 -, - Jd) rfTfz) chi0 b $ -v - y1 V , - ™ - «« ll 0 5 0 5 0 5 where hi is the controlled layer thickness; H b - a. E is the inner radius of the ring; b is the outer radius of the ring; "D is the central angle in the lock of the ring, which is in an unclean state; n is the total number of layers; y is the work of adhesion at the boundaries of the layers; E |, / l, Eo, modulus of elasticity and Punch coefficient for the materials of the layer and ring, respectively; Oo is the coefficient of thermal expansion of the ring; T (2) is the temperature distribution over the thickness of the ring; . yi I fr, $ take into account the thickness of the layer hi and the elastic characteristics of the layer and ring; / i, 5i - take into account the thickness of the layer h; and thermal expansion coefficients of the layer and ring; ci (Z) is the concentration of atoms introduced into the interstitial site; Rni is the radius of the pore in the lattice of the layer; Rnp is the radius of the implanted atom; P is the pressure exerted by the walls of the cylinder on the ring; T (b) is the temperature on the outer surface of the ring; M.N - take into account the geometric dimensions of the ring. Table 1 table 2 oi g b t s 6 t 8 s y ii That / idin coating, N, microns Fie. 2 Figure 1 0-7 1-2 2-3 3-4 4-S 500 No. W Yu& L L Fig.Z 1118 Spew