Printer-friendly version
Glossary of MinSE


Browse the glossary using this index

Special | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O
P | Q | R | S | T | U | V | W | X | Y | Z | ALL

Page:  1  2  (Next)
  ALL

H

:

A term usually referring to transition metal carbides and nitrides deposited by CVD or plasma assisted PVD methods, e.g., TiC and TiN, which have Vickers hardness values in excesss of 2000 kg/mm2.   The term hard coating tends to be invoked when these coatings are being applied in order to improve wear resistance of various items,  e.g., metal cutting tools or bio-medical prosthetic implants.

Hungary flag Kemény bevonat

:

Jargon for hard chromium or hard nickel plating, but usually the former.

Hungary flag Kemény lemezelés, bevonás

:

Qualitatively, a measure of the resistance of a surface to penetration by an indenter. Quantitatively, a measure of yield strength. For example, Vickers hardness Hv is related to yield strength (sy) by the approximate relationships:

Hv ≈ 3 sy (for metals and alloys)

Hv ≈ 4 sy (for ceramics)

Hungary flag keménység

:

Various methods of hardness determination exist.  These can be broadly grouped into: (i) static and; (ii) dynamic hardness methods.  In surface engineering only static methods are used.   These comprise Vickers, Knoop and Berkovich diamond indentation methods.   Rockwell hardness on scales A, B or C is used in accordance with the type of material; most popular in the United States and unsuited to microhardness determination.   See Vickers hardness, Knoop hardness, and Berkovich indentation hardness.

Hungary flag Keménység mérés

:

Also sometimes termed hardness distribution.  In surface engineering it specifically refers to microhardness as a function of depth below the surface.   The shape and magnitude of such curves are often a signature of a given type of treatment.   "S" shaped curves are a characteristic feature of nitrided or carburised steels (see below) while single step-like curves are typical of hard coated ferrous or non-ferrous alloys.   Hardness profiles are most easily determined using Vickers or Knoop hardness  indentation methods.  Also see Vickers hardness, Knoop hardness, Berkovich indentation hardness  and nanoindentation hardness.

Hungary flag Keménység eloszlás

:

The manipulation of bulk and surface properties of a material by the concise application of heating and cooling cycles, in an appropriate atmosphere.  For steels, comon bulk heat treatments include, annealing, hardening & tempering, normalising, stress relieving and sub-critical annealing.   Some common "surface heat treatments", include carburising, nitriding, nitrocarburising and boriding

Hungary flag hőkezelés

:

In surface engineering this refers to the HAZ beneath a power beam alloyed or clad surface, i.e., the zone, adjacent the formerly liquid region, which remained in the solid state for the entirety of the treatment, but whose microstructure has been changed from that of the core, as a result of rapid heating and cooling.

Hungary flag tűzi ónozási zóna

:

Cone cracks formed on the surface of a brittle elastic solid (e.g., ceramics and glass) resulting from the high contact stresses exerted during point contact loading by a spherical indenter (or similar).    Note: in sliding contacts ring shaped cracks are replaced by a series of overlapping arc-shaped cracks.   This effect can also be seen following scratch testing.

Hungary flag Hertz repedések

:

A situation whereby a high yield strength and/or high modulus coating fails through plastic flow of a low yield strength substrate during intensive point contact loading (diagram).   Sometimes referred to as the "thin ice effect".   Also see Hertzian stresses.

Hungary flag Hertz törés

:

The Hertzian elastic contact stresses developed, for example, when an indenter contacts a planar surface. The shape of the elastic stress field and the position of the maximum resolved shear stress depends upon indenter geometry, while the magnitude of the compressive and shear stresses (for a given contact force) is dependent upon the elastic moduli and Poissons ratios of the indenter and planar materials. For a spherical indenter, indenting a planar surface, the radius of circular contact (a) is given by:

a = (3FR/4E*)1/3

where:

F = Applied load (N)

R = radius of the indenter (m)

R = radius of the indenter (m)

E* = ((1-u12/E1) + (1-u22/E2)) -1

E1 = indenter Young's modulus (G.Pa); u1 = Poissons ratio of indenter

E2 = Young's modulus of the semi-infinite surface (G.Pa); u2 = Poissons ratio of semi- infinite surface

The maximum contact pressure Pm (M.Pa) at the contact interface is given by:

Pm = (3F/2pa2) = (6FE*2/p3R2)1/3

The shear stress t is zero at the contact interface but achieves its maximum value along the indenter centre line at a position that is exactly 0.48a beneath the planar surface. The magnitude of tmax (M.Pa) is simply related to Pm:

tmax = 0.31 Pm

For a cylinder contacting a planar surface the Hertzian equations are modified, but it is worth noting that tmax = 0.30 Pm (very close to the relationship for a spherical indenter), whereas, the position of the maximum shear stress, is exactly 0.78a beneath the planar surface. Hence, when considering tribological situations where third body particles are present, the particle (or indenter) shape has a very strong influence on the position of the maximum shear stress. This has implications for coating design specifications. Coating "X" maybe of adequate thickness for avoiding sub-surface yielding by spherical particles, but maybe inadequate for avoiding sub-surface yielding by cylindrical or rod-shaped particles. For a more rigorous mathematical analysis the reader is referred to K. L. Johnson's, "Contact Mechanics", Cambridge University Press, 1987.

Hungary flag Hertz feszültség


Page:  1  2  (Next)
  ALL


Theme by NewSchool Learning