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Estimation of synergism of surface engineering technology
T. Burakowski
Technical University of Radom, Radom, 26-600, Poland Institute of Precision Mechanics, Warsaw, 00-967, Poland
In the paper the author definition of influence coefficient, synergism and synergism coefficient has been presented. The paper includes examples of synergism measuring based on experimental research.
1. Introduction
The term of synergism is quite old. Firstly it appeared in catholic theology, and later on it was adopted by pharmacology, medicine, social sciences, chemistry and technical sciences. Unfortunately, the term was vaguely formulated and interpreted in many ways. Moreover, there was no way to quantify it. In this report I suggest a more scientific approach to the problem.
2. Interaction of system elements
Elements of any systems are subject to their interactions. There can be two or more elements and their interactions influence the system properties. To quantitatively define the ultimate effect of two (or more) system factors (e.g. surface engineering technologies: nitriding and TiN coating) on a given property, I suggest introduction of the influence coefficient [1]:
a
ki =—, aI
where ai is the property obtained as a result of influence of one factor (e.g. service-life of a given part after nitriding), a is the same property obtained as a result of influence of two elements of the system (e.g. service-life of the nitrided part and TiN coating).
The influence coefficient ki is therefore a multiply of a change of property a under the influence of two or more factors related to the same property aI under one factor only. The ki coefficient value may be positive, equal to zero or negative. The value of the coefficient reflects the effectiveness of the influence.
Generally, the influence of the factors may be constructive, neutral or destructive, i.e. increase the overall effect (synergism), have no effect (neutralism) or decrease the overall effect (antagonism). Therefore I suggest to assign to the kI coefficient names related to its value (Fig. 1):
- synergism coefficient kI = kS > 1 — the higher the value of kS ^ the higher synergism (intensity of the positive influence),
- neutralism coefficient kN = kI = 1 — for kI there is no influence,
Fig. 1. Graphic interpretation of coefficients of synergism, neutralism and antagonism of a property
T. Burakowski, 2004
Synergism coefficient kSa = g- >1
complete a > (a1 + a2) additive a = <aT + a2) incomplete a < (a, + a2)
a- a2 a -Я2 -Si ai a2 a -az -ai ai ai -02 - ai
Fig. 2. Graphic interpretation of complete, additive and incomplete syner-gizm of a property; at is the property obtained as a result of action of the first factor; a2 is the property obtained as a result of action of the second factor; a is the property obtained as a result of action of the both factors
- antagonism coefficient kA = kY < 1 — the lower the value of kA ^ the higher antagonism (intensity of the negative influence).
3. The idea of synergism and synergism coefficient
As far as surface engineering is concerned I propose the following definition of synergism (which can be also extended to cover other technical sciences).
Synergism is a reciprocal co-operation of two or more factors, elements, substances, technologies of production or service generated ones either more effective than a simple sum of their separate actions (effects) or equal to that sum (additivity), or sometime even less effective but always greater than a separate action of one factor. In all these cases the new properties can be obtained, never appearing when one factor would act only.
It seems to be correct to call the first type of syner-gism — complete synergism, the second one — additive synergism, and the third one — incomplete synergism. The complete synergism can be also considered as limited, strict notion while the incomplete synergism has a wider reference. The first one appears very rarely, the second one very often
(Fig. 2).
The synergetic effect may be expressed by one property of a system (e.g. resistance), this is called a single-property synergism. If the effect is expressed by many properties (e.g. hardness, corrosive resistance, wear), this is a multi-property synergism.
For synergism to occur, there must be at least two factors, e.g. two technologies. When there are more factors in effect, e.g. technologies, actions, processes — a multifactor synergism exists. As a result of action of two or more factors usually one or more properties of a system change, but in many directions. If there is increase of the numerical value of the property the co-operation of factors is called syner-gism, if there is decrease of the value of the property — antagonism. The property may remain unchanged — in such
situation neutralism takes place. We should mention that the increase of the numerical value of a particular property is not always desirable (e.g. wear), and decrease — undesirable. Either the increase or decrease is desirable depends on the property examined, e.g. it is favorable to decrease the temperature of thread milling cutter as a result of applying two or more surface engineering technologies and consequently to decrease wear and increase service-life [2].
The synergetic effect (also neutralistic or antagonistic one) can appear as an influence on one property of the system but also on many properties of the system, and it happens in majority of cases.
Multiproperty synergism similarly to single-property synergism, can be complete, additive or incomplete. In general case of multiproperty system there can occur synergism for the first property, neutralism for the second property and antagonism for the third property, so the synergism coefficient for different properties can have various values (a, b, ..., n), e.g. ka > 1, kb = 1, kn < 1. For instance, two-factor (two technologies), two-property synergism (hardness, plasticity) of hardening + tempering technology is negative (antagonism) for hardness (kH < 1) and positive (synergism) for plasticity (kA > 1), because as a result of hardening high hardness H and low plasticity A are obtained. Due to subsequent tempering hardness Hminimally decreases and plasticity A increases significantly.
4. Synergetic properties and factors
The properties of superficial layers, both potential and usable as well as suitable properties for coatings are well known in literature [1]. To each of these properties (a, b, ..., n) a suitable coefficient of synergism can be assigned. Such coefficient could be enlarged with an adjective (or noun) to describe each property, e.g.:
for a = hardness: synergism coefficient of hardness,
khard,
for b = thickness: synergism coefficient of thickness,
kthick,
for c = strength: synergism coefficient of strength, kstren, for d = corrosion resistance: synergism coefficient of corrosion resistance, kcor,
for e = tribological wear: synergism coefficient of tribo-logical wear, k^,
forf= service-life: synergism coefficient of service-life,
ksl, etc.
5. Exemplification of synergism of technologies in surface engineering
Synergism of technologies has been known for a long time, and the higher the level of technique and technologies is the more distinctly it appears (Fig. 3).
Almost all technologies of heat treatment known and applied already in antiquity had the synergetic character. Usually quench hardening or quenching (austenizing + coo-
Fig. 3. Synergism of technologies: essence and goal
ling) is not applied without tempering. Hot hardening = quenching + low-temperature tempering; toughening = quenching + high or medium temperature tempering; precipitation hardening = solution treatment + ageing.
Electrolytic coatings are applied on degreased and chemically activated surfaces (e.g. phosphatizing) and usually first the round coating (e.g. Cu) is applied and then the surface coating (e.g. Ni) is deposited. The similar procedure is with varnishing.
The most modern technologies of surface engineering require the particular preparation of the surface: besides cleaning and degreasing or washing and degreasing also ion etching is applied before coating.
The most common example of combination of technologies is the connection of technology of base forming without special preparation of a superficial layer (a superficial layer always exists) or with the special preparation of a superficial layer with one or more layers of coating. There are many possibilities to create superficial layers and coatings but it is necessary to remember that combinations of generating superficial layers on the same core make technical sense, while generating coats only does not make such sense; the coatings must always be applied on the superficial layers of the core.
It follows clearly from the above that the main aim of synergism is to obtain better potential or usable properties (one or more) of technological surface layers (TSL) or service-generated surface layers (SSL) (see Fig. 3).
In the literature synergism is presented in various ways, usually without using the word "synergism" and mainly describing the properties obtained by means of one technology with or without special preparation of the core in function of one or more parameters. Very often the increase of properties in relation to the basic technology or without this relation, is described.
In both cases the increase of properties (or multiple of this increase) is simply the synergism coefficient of the respective properties.
Regardless of the type of the property or synergetic factors all synergism coefficients can be expressed either in situation of increase or decrease of the property value.
6. Some examples of the synergism coefficient
It is practically the most common situation that the effect of the action of synergetic factors is beneficial when the value of a given property increases, i.e. when a > az and the total effect is higher in value than the effect caused by one factor only. Such properties can be for instance: service-
14
„,-12
| 10
Si о
о
a> %2
Numerals indicate a number of holes (intermediate - midd I-1 drilled (twist drill 10,2) e service-lite) 210
3 tapped (screw-top M12)
220
SL- supericial layer
С - coating l/U
z m u + 7
250
2 z Й < О + tn 220
i 4 160 N Ё О + rn
г £ IbO t d + w -la 55 F О + -j ю
50 a 20 * -2L_
l Г»
Fig. 4. Synergism coefficient of service-life drills and screw-tops of systems: core (HSS SW7M) — coating (different nitride); stock — iron Zl 250, cutting fluid — Emulgel 42; based on the data of [3]
Fig. 5. Synergism coefficient of service-life of screw-top with coatings: (Ti, Zr)N and Ti(C, N); based on the data of [4]
Fig. 6. Graphic interpretation of defining of triple factor (high speed tool steel, high speed tool steel with TiN coating, high speed tool steel with TiN and TiC coatings) synergism of temperature decrease of a thread milling cutter made of high speed tool steel; based on the data of [5]
life, corrosive resistance, fatigue strength, wear resistance, hardness, barrier properties (thermal, acoustic etc.).
In such situations the synergism coefficient is defined as the ratio of experimentally acquired property values — expressed for instance in units, millimeters, temperature degrees — to initial values of the particular properties. This ratio is the synergism coefficient of the increase of the specified property, e.g. service-life of drills and screw-tops (Figs. 4, 5). Simplifying, one may call it conventionally the synergism coefficient of increase.
It is a relatively rare situation when the effect of the action of synergetic factors is positive when the value of the examined property decreases, i.e. a < aI and the total effect is lower in value than the effect caused by one factor only. Such properties can be for instance: tribological wear, temperature of thread milling cutter.
Formally such a situation (the decrease of the value!) is an antagonism, but a favorable one. The antagonism coefficient is the reciprocal of the synergism coefficient. Therefore defining the antagonism coefficient, one may treat its reciprocal as the synergism coefficient but not of increase but of decrease of the value of a given property. Simplifying, one may call it conventionally the synergism coefficient of decrease.
Figure 6 demonstrates the synergism coefficient defining based on examples from milling technologies: decrease of thread milling cutter temperature in effect of applying one or two antiwear coatings.
7. Conclusion
1. Synergism exists in nature regardless of our will in effect of self-organization of the matter: extortion (co-ope-
ration) ^ answer. In surface engineering technologies it is possible to take advantage of the synergetic co-operation of technologies to maximize the total synergetic effect, i.e. to maximize synergism coefficient of the increase of the desirable property or of the decrease of undesirable one.
2. One of the dynamic directions of the development of the surface engineering is the combination of different technologies of surface layer formation, that is multiplex technology, to obtain their multiproperty synergism.
3. Understanding the essence of synergism and syner-getic coefficients is useful when dealing with two or more technology co-operating. Using the term of property synergism coefficient as the ratio of the variations of this property enables a comparison of technology co-operation from various aspects (various properties). It seems to be true that the idea of synergism coefficient may be successfully applied not only in surface engineering technologies.
References
[1] T. Burakowski, Rozwazania o Synergizmie — Synergizm w Inzynierii Powierzchni, Wyd. Politechniki Radomskiej, Radom, 2004 (in print).
[2] T. Burakowski, The Proposal of Determining Quantitative Synergism in Surface Engineering, in Proc. of 3rd International Conference on Surface Engineering, Oct. 10-13 2002, Southwest Jiaotong University, Chengdu, China (2002) 193.
[3] M. Kupczyk, Inzynieria Powierzchni — Powloki Przeciwzuzyciowe na Ostrza Skrawajace, Wyd. Politechniki Poznanskiej, Poznan, 2004.
[4] T. Burakowski, A. Mazurkiewicz, K. Miernik, J. Walkowicz, Wykor-zystanie osiagniec inzynierii powierzchni w badaniach naukowych i aplikacjach, in VIIIKrajowy Kongres Urzadzen Technicznych, Krynica 23-26.09 1997, Druk, "Tribologia", 5-6 (1997) 486.
[5] P. Kula, Z. Gawronski, D. Siniarski, J. Sawicki, Designing of structure and properties of composite coatings for special applications, in Proc. of 12th Summer School "Modern Plasma Surface Technology", Ko-lobrzeg, May 2000.
