Vickers hardness test 1552505 220183785 2008-06-18T17:45:26Z 77.212.27.18 /* References */ [[Image:Vickers-tester.png|thumb|A Vickers hardness tester]] The '''Vickers hardness test''' was developed in the early 1920s as an alternative method to measure the [[hardness]] of materials. The Vickers test is often easier to use than other hardness tests since the required calculations are independent of the size of the indenter, and the indenter can be used for all materials irrespective of hardness. The basic principle, as with all common measures of hardness, is to observe the questioned materials' ability to resist plastic deformation from a standard source. The Vickers test can be used for all [[metal]]s and has one of the widest scales among hardness tests. The unit of hardness given by the test is known as the '''Vickers Pyramid Number (HV)'''. The hardness number can be converted into units of Pa, but should not be confused with a pressure, which also has units of Pa. The hardness number is determined by the load over the surface area of the indentation and not the area normal to the force, and is therefore not a pressure. The hardness number is not really a true property of the material and is an empirical value that should be seen in conjunction with the experimental methods and hardness scale used. When doing the hardness tests the distance between indentations must be more than 2.5 indentation diameters apart to avoid interaction between the work-hardened regions. The yield strength of the material can be approximated as : <math>H_V = c {\sigma_y}\approx {3}{\sigma_y}</math>. where c is a constant determined by geometrical factors usually ranging between 2 and 4. == Implementation == [[Image:Vickers-path.svg|thumb|Vicker's test scheme]] The Vickers hardness test uses a [[diamond]], with the shape of square-based pyramid with an angle of 136° between opposite faces as an indenter (22° between the indenter face and surface). It is based on the principle that impressions made by this indenter are geometrically similar regardless of load. Accordingly, loads of various magnitudes are applied to a flat surface, depending on the [[hardness]] of the material to be measured. The Vickers Pyramid Number (HV) is then determined by the ratio '''F/A''' where '''F''' is the force applied to the diamond and '''A''' is the surface area of the resulting indentation. '''A''' can be determined by the formula : <math>A = \frac{d^2}{2 \sin(136^{\circ}/2)}</math>, which can be approximated by evaluating the sine term to give : <math>A \approx \frac{d^2}{1.854}</math>, where ''d'' is the average length of the diagonal left by the indenter. Hence, : <math>H_V = \frac{F}{A}\approx \frac{1.854 F}{d^2}</math>. The corresponding units of HV are then [[kilogram-force]] per square millimetre (kgf/mm²). To convert a Vickers hardness number in SI units (MPa or GPa) one needs to convert the force applied from kgf to newtons and the area from mm<sup>2</sup> to m<sup>2</sup> to give results in pascals (1 kgf/mm² = 9.80665×10<sup>6</sup> Pa). A practical method to convert HV to SI units: <div style="width: 75%; padding: 7px; background: #c2f4f5; border: 1px solid black; margin: 0 auto; text-align: center;">''To convert HV to MPa multiply by 9.807''<br/> ''To convert HV to GPa multiply by 0.009807''</div> Vickers hardness numbers are reported as '''xxxHVyy''', e.g. '''440HV30''', where: * '''440''' is the hardness number, * '''HV''' gives the hardness scale (Vickers), * '''30''' indicates the load used in kg. == Examples == Some HV values<ref>Smithells Metals Reference Book, 8th Edition, ch. 22</ref> * Stainless Steels 140-180HV30 (316L & 347L stainless respectively) * Carbon Steel 55-120HV5 (Note: load is different from that of stainless) * Iron 30-80HV5 <gallery> Image:Case hardened steel-vickers hardness test.png|Case Hardened Steel - Rapid Quench - Vickers Hardness Test </gallery> == References == <references/> * {{cite book | author = Meyers and Chawla | year = 1999 | chapter = Section 3.8 | title = Mechanical Behavior of Materials | publisher = Prentice Hall, Inc }} * [http://www.gordonengland.co.uk/hardness/vickers.htm Vickers hardness test] on Gordon England site. * [http://www.struers.com/default.asp?top_id=5&main_id=25&doc_id=344&target=_self&collapse=1 Struers hardness conversion table] * "Metallographic and Materialographic Specimen Preparation, Light Microscopy, Image Analysis and Hardness Testing", Kay Geels in collaboration with Struers A/S, ASTM International 2006. == See also == * [[Hardness (materials science)]] * [[Brinell hardness test]] * [[Rockwell scale]] * [[Knoop hardness test]] * [[Hardness comparison]] * [[Ceramography#Microindention_Hardness_and_Toughness | Vickers indention of ceramics]] [[Category:Hardness tests]] [[cs:Zkouška tvrdosti podle Vickerse]] [[de:Härte#H.C3.A4rtepr.C3.BCfung_nach_Vickers]] [[es:Dureza Vickers]] [[it:Scala Vickers]] [[nl:Vickers (hardheid)]] [[ja:ビッカース硬さ]] [[pl:Skala twardości Vickersa]] [[pt:Dureza Vickers]] [[ru:Метод Виккерса]] [[sv:Vickersprovning]] [[zh:维氏硬度试验]]