硬度是材料机械性能重要指标之一，而硬度试验是判断材料或产品零件质量的一种手段。所谓硬度，就是材料在一定条件下抵抗另一本身不发生残余变形物体压入能力。抵抗能力愈大，则硬度愈高，反之则硬度愈低。在机械性能试验中，测量硬度是一种最容易、最经济、最迅速的方法，也是生产过程中检查产品质量的措施之一，由于金属等材料硬度与其他机械性能有相互对应关系，因此，大多数金属材料可通过测定硬度近似地推算出其他机械性能，如强度、疲劳、蠕变、磨损和内损等。所以硬度计被广为应用。
一、显微硬度计工作原理和组成
显微硬度计是近年来常用测量硬度的设备。测量硬度是通过升降显微硬度计的调焦机构、测量显微镜、加荷机构，正确选择负荷、加荷速度进行全自动加卸试验力及正确控制试验力保持时间，通过显微硬度计光学放大，测出在一定试验力下金刚石角锥体压头压入被测物后所残留压痕的对角线长度，来求出被测物硬度值。
二、显微硬度计的正确使用
由于显微硬度试验往往是对很小的试样（如针尖)，或试样上很小的特定部位（如金相组织）进行硬度测定，而这些情况难以用人眼来进行观察和判定，而且显微硬度试验后所得压痕非常小，这也是难以人眼来寻找，更不用说进行压痕对角线长度的测量，所以非得用显微镜才能进行工作。正确使用显微硬度计，除了正确选择负荷、加荷速度、保荷时间外，测量显微镜使用的正确与否是十分重要的。现就如何正确使用显微硬度计作简要介绍。
1.负荷的选择
为确切得到被测对象的真实硬度，必须选择恰当负荷。选择负荷应考虑以下几个原则:
(1)在测定薄片或表面层硬度时，要根据压头压入深度和试件或表面层厚度选择负荷。因为一般试件或表面层厚度是知道的，而被测部位硬度或硬度范围也应是可知道的，基于压头压入试样时挤压应力在深度上涉及范围接近于压入深度的10倍，为避免底层硬度的影响，压头压入深度应小于试件或表面层的十分之一。
(2)对试样剖面测定硬度时，应根据压痕对角线长度和剖面宽度选择负荷。基于压头压入试样时产生的挤压应力区域最大可从压痕中心扩展到4倍对角线的距离。为避免相邻区域不同硬度或空间对被测部位硬度影响，所以压痕中心离开边缘的距离应不小于压痕对角线长度的2.5倍，即压痕对角线长度为试件或表面层剖面宽度的五分之一。
(3)当测定晶粒、相、类杂物等时，应遵守以上两个原则来选择负荷，压头压入深度不大于其厚
度的1/10，压痕的对角线长度应不大于其面积的1/5.
(4)测定试件(零件、表面层、材料)平均硬度时，在试件表面尺寸及厚度允许的前提下，应尽
量选择大负荷，以免试件材料组织硬度不均匀影响试件硬度测定的正确性。
(5)为保证测量精确度，在情况允许时，应选择大负荷，一般应使压痕对角线长度大于20μ m。
(6)考虑到试件表面冷加工时产生的挤压应力硬化层的影响，在选择负荷时应在情况许可的情况
下选择大负荷。
2.测量显微镜的正确使用
(1)寻找像平面
1)针尖试样应采用“光点找像法”。
一般显微硬度计测量显微镜物方视场只有0.25~0.35mm,在此视场范围外区域，在测量显微镜目镜视场内，眼睛是看不见的。而针尖类试样项尖往往小于0.1mm,所以在安装调节试样时，很难把此顶尖调节在视场内:如果此顶尖在视场周围而不在视场内，则在升降工作台进行调节时不小心就会把物镜镜片顶坏，即使不顶坏物镜，找像也很困难，为解决这个问题，提出“光点找像法”方法。开启测量显微镜的照明灯泡，这时在物镜下面工作台，上就有一个圆光斑，把针尖试样垂直于工作台安装在此光斑的中心，升高工作台，使此针尖的顶尖离开物镜约1mm,这时眼睛观察顶尖部位，调节工作台.上的两个测微丝杆，使物镜下照明光点在前后左右对称分布在此顶尖上(这-步骤必须仔细),随后缓慢调节升降机构，这时在目镜视场中即会看到-一个光亮点，这就是此顶尖上的反射光点，再进一步调节升降即可找到此针尖的像。
(3)当测定晶粒、相、类杂物等时，应遵守以上两个原则来选择负荷，压头压入深度不大于其厚度的1/10，压痕的对角线长度应不大于其面积的1/5.
(4)测定试件(零件、表面层、材料)平均硬度时，在试件表面尺寸及厚度允许的前提下，应尽量选择大负荷，以免试件材料组织硬度不均匀影响试件硬度测定的正确性。
(5)为保证测量精确度，在情况允许时，应选择大负荷，一般应使压痕对角线长度大于20μ m。
(6)考虑到试件表面冷加工时产生的挤压应力硬化层的影响，在选择负荷时应在情况许可的情况下选择大负荷。
2.测量显微镜的正确使用
(1)寻找像平面
1)针尖试样应采用“光点找像法”。
一般显微硬度计测量显微镜物方视场只有0.25~0.35mm,在此视场范围外区域，在测量显微镜目镜视场内，眼睛是看不见的。而针尖类试样项尖往往小于0.1mm,所以在安装调节试样时，很难把此顶尖调节在视场内:如果此顶尖在视场周围而不在视场内，则在升降工作台进行调节时不小心就会把物镜镜片顶坏，即使不顶坏物镜，找像也很困难，为解决这个问题，提出“光点找像法”方法。开启测量显微镜的照明灯泡，这时在物镜下面工作台，上就有一个圆光斑，把针尖试样垂直于工作台安装在此光斑的中心，升高工作台，使此针尖的顶尖离开物镜约1mm,这时眼睛观察顶尖部位，调节工作台.上的两个测微丝杆，使物镜下照明光点在前后左右对称分布在此顶尖上(这-步骤必须仔细),随后缓慢调节升降机构，这时在目镜视场中即会看到-一个光亮点，这就是此顶尖上的反射光点，再进一步调节升降即可找到此针尖的像。
2)表面光洁度很高的试样( 如显微硬度块)应采用边缘找像法.
显微硬度试验中，试样表面光洁度一般都是很高的，往往是镜面，表面上没有明显观察特征，而显微硬度计中所有高倍测量显微镜的景深都是非常小的，只有1~7μm，所以在调焦找像平面时，对于缺乏经验的操作者是很困难的，甚至会碰坏物镜，所以操作者有的留用表面残留痕迹来找像平面，但有时往往无残留痕迹时，建议采用边缘找像法。即按上述同样方法使用照明光点(约为0.5~-.1mm)的中心对准试样表面轮廓边缘，则在且镜视场内看到半亮半暗的交界处即为此轮廓边缘，随后进-步调节升降即可找到此表面边缘的像。
(2)调节照明
为防止倾斜照明对压痕对角线长瘦测量精确度的影响，要调节照明光源，使压痕处在视场中心时按两对角线区域分的四个区间亮度一致，通过观察测微目镜视场内压痕像的清晰程度，可将照明光源经上、下、前、后、左、右方向稍稍移动，直至观察到压痕像最明亮，没有阴影为止:移动工作台微分筒将压痕像前、后、左、右移动，测微目镜视场内均应明亮,没有阴影的压痕像为好。
(3) 视度归正
我们知道测量显微镜测压痕时，是把压痕经物镜放大后，成像在目镜前分划板上，进行瞄准测量。由于人眼视差异(如正常眼、近视眼、远视眼)，作为放大镜作用的目镜必须放在各种不同位置，才能对分划板的刻线作清楚观察(即刻线这时为最“细”),这个步骤(调节目镜相对于分划板距离)称为视度归正，不然会影响测量正确性。
(4)压痕位置的校正
通过试验力载荷在测微目镜视场看到的压痕像，若其偏移视场中心较大，则需要进行压痕位置校正，通过物镜座几个调整螺钉反复调整，直到在测微目镜视场内压痕像居中为止此.G调整]D个螺钉时不要移动工作台)并相互锁紧。
(5)调焦
为找到正确成像位置，应注意要调节使压痕边缘清晰，而不是压痕对角线或对角线交点清晰.我们需要测量的是这个四棱角锥体坑表面棱形的对角线长度。为帮助操作者掌握这一步骤，这里提出“视差判别法”，当用分划板刻线或十字交点对准压痕对角线顶尖时，人眼相对于目镜左右移动，这时如调焦不正确，即压痕边缘象不完全落在分划板上，则会发现此边缘相对于分划线会左右移动。这说明调焦不正确，如人眼相对目镜的位置不一致，则一定存在测量误差，此时应进一步调焦， 直至此边缘相对分划线在人眼晃动时无相对位置才为正确。
三掌握正确的测量方法
1、旋转测量目镜，使分划板的移动方向和待测压痕对角线方向平行，这样可避免两者夹角对测量精确度的影响。如两者来角为C实际长度为，EO则测得长度d’: d/osc, 而且对于用十字线交点瞄准压痕对角线顶朱览当两者有一交角时载会造成其对角线- -端顶尖对准十字线交点时，另一端顶尖则不能对准。
2、测量压痕对角线长度，在瞄准时必须瞄准压痕对角线的两端顶尖,不必考虑压痕棱形四边情况。这对于分划板上刻线是直线的情况是不成问题的，而对于分划板上刻线是十字线，瞄准压痕棱边还是对角线顶尖的争论时常发生，为统一各种 分划线的瞄准，所以确定了这- -原则，这样也可解决棱边多种多样复杂情况下的瞄准问题.
3、测量中应注意的几个问题
(1)机械式测微机构测量目镜，测量时应单向转动测微手轮，消除空回对测量的影响..
(2)对于同时测定型的测微目镜，操作者应注意两块分划板刻线重合时，测微读数零位是否正确，如不正确，应规正微分简或测量后加以读数修正。
(3)对数字式测微目镜，在每次开机后应使两块分划板刻线重合，然后按按“清零键" 使读数清零。
(4)当压痕两条对角线长度不等时，应测量两条对角线长度并取其平均值.
(5)在旋转测量显微目镜使其分划板的移动方向和压痕待测对角线平行后，可在此对角线垂直方向.上移动工作台，使对角线落在分划板十字线交点移动的轨迹上，但在用此交点进行瞄准时，则应转动测微目镜的手轮，而不应移动工作台。
(6)操作人员应严格训练，经常以标准显微硬度块校验自已的瞄准精确度.
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Hardness is one of the important indexes of material mechanical properties, and hardness test is a means to judge the quality of material or product parts. The so-called hardness, is the material under certain conditions to resist another itself does not occur residual deformation of the object pressed into the ability. The higher the resistance, the higher the hardness, vice versa. In mechanical properties test, hardness measurement is one of the most easy way, the most economical, most quickly, is also one of the measures to check the quality of the products in the process of production, such as metal material hardness and other mechanical properties have a corresponding relation between each other, therefore, most metal materials can be approximately calculated by measuring hardness other mechanical properties, Such as strength, fatigue, creep, wear and internal loss, etc. So the hardness tester is widely used.
First, micro hardness tester working principle and composition
Microhardness tester is commonly used to measure hardness equipment in recent years. Measuring hardness is through the platform of microhardness meter focusing mechanism, measuring microscope, load, correct selection of load and the loading speed for automatic unloading test force and control test force to keep time correctly, by microhardness meter optical amplifier, measured under a certain test force diamond pyramid head pressing into the material being tested by the residual indentation diagonal length, To figure out the hardness of the object being measured.
Two, the correct use of microhardness tester
Because microhardness test is often on a small sample (tip), or on a specific part of the small sample hardness measurement, such as microstructure, and the situation is difficult to choose and employ persons eye for observation and judgement, and micro hardness test after the indentation is very small, it is also difficult to the human eye to look for, not to mention the indentation diagonal length measurement, So you have to work with a microscope. In order to use microhardness tester correctly, it is very important to choose the correct load, loading speed and holding time. This paper introduces how to use microhardness tester correctly.
1. Load selection
In order to obtain the true hardness of the tested object, the appropriate load must be selected. The following principles should be considered in the selection of load:
(1) When determining the hardness of thin section or surface layer, the load should be selected according to the depth of the indenter and the thickness of the specimen or surface layer. Because general specimens or know, is the thickness of surface layer and the measured parts hardness or hardness range should be know, based on the pressure head into sample extrusion stress in depth range close to 10 times the depth of press in, to avoid the influence of hardness, depth of head pressure should be less than one over ten of the specimen or surface layer.
(2) When determining the hardness of the sample profile, the load should be selected according to the diagonal length of the indentation and the width of the profile. Based on the indenter pressed into the sample, the compressive stress region can extend from the center of the indentation to a maximum distance of 4 times the diagonal. In order to avoid the influence of different hardness or space in adjacent areas on the hardness of the measured part, the distance between the indentation center and the edge should not be less than 2.5 times the length of the indentation diagonal, that is, the length of the indentation diagonal is 1/5 of the width of the specimen or surface layer profile.
(3) When determining grain, phase, sundry, etc., the above two principles should be followed to select the load, the depth of the head is not greater than its thickness
Degree of 1/10, the length of the diagonal indentation should not be greater than 1/5 of its area.
(4) When measuring the average hardness of the specimen (parts, surface layer, material), the surface size and thickness of the specimen should be used under the premise of allowing
Large load is selected to avoid the uneven hardness of specimen material structure affecting the accuracy of hardness measurement.
(5) in order to ensure the accuracy of measurement, when the situation allows, should choose a large load, generally should make the indentation diagonal length greater than 20μ m.
(6) Considering the influence of the extrusion stress hardening layer on the surface of the specimen during cold processing, the load selection should be under the condition that conditions permit
Under select large load.
2. Proper use of measuring microscope
(1) Find the image plane
1) Tip sample should adopt "light spot image finding method".
General microhardness tester measuring microscope object square field of view is only 0.25~0.35mm, in this field outside the area, in the field of view of the measuring microscope eyepiece, the eye is invisible. And needlepoint class sample items are often less than 0.1 mm, so when installing a control sample, it is difficult to adjust the top in the field: if the top around the field and not in the field, when making adjustment in the platform will not carefully the objective lens very bad, if not the top bad objective, find like is hard, in order to solve this problem, the "spot to find like method" is proposed. Turn on the lighting bulb of the measuring microscope, then there is a round spot on the table below the objective lens, install the tip sample perpendicular to the table in the center of the spot, raise the table, make the tip tip leave the objective lens about 1mm, then observe the top part of the eye, adjust the table. The two on the micrometer screw, make objective under illumination light spot on the left and right sides is symmetrical distribution in the top before and after (this step must be carefully), then slowly adjust the lifting mechanism, then will see in the eyepiece - a light point, this is the reflection on the top spot, further adjust the lift can find like this tip.
(3) when determining grain, phase, sundry, etc., should comply with the above two principles to choose the load, the depth of the head is not greater than 1/10 of its thickness, the diagonal length of the indentation should not be greater than 1/5 of its area.
(4) When measuring the average hardness of specimens (parts, surface layer and materials), under the premise of allowing the surface size and thickness of specimens, large load should be selected as far as possible, so as to avoid the uneven hardness of specimen material structure affecting the accuracy of hardness measurement of specimens.
(5) in order to ensure the accuracy of measurement, when the situation allows, should choose a large load, generally should make the indentation diagonal length greater than 20μ m.
(6) Considering the influence of the extrusion stress hardening layer on the surface of the specimen during cold working, large load should be selected if the situation permits.
2. Proper use of measuring microscope
(1) Find the image plane
1) Tip sample should adopt "light spot image finding method".
General microhardness tester measuring microscope object square field of view is only 0.25~0.35mm, in this field outside the area, in the field of view of the measuring microscope eyepiece, the eye is invisible. And needlepoint class sample items are often less than 0.1 mm, so when installing a control sample, it is difficult to adjust the top in the field: if the top around the field and not in the field, when making adjustment in the platform will not carefully the objective lens very bad, if not the top bad objective, find like is hard, in order to solve this problem, the "spot to find like method" is proposed. Turn on the lighting bulb of the measuring microscope, then there is a round spot on the table below the objective lens, install the tip sample perpendicular to the table in the center of the spot, raise the table, make the tip tip leave the objective lens about 1mm, then observe the top part of the eye, adjust the table. The two on the micrometer screw, make objective under illumination light spot on the left and right sides is symmetrical distribution in the top before and after (this step must be carefully), then slowly adjust the lifting mechanism, then will see in the eyepiece - a light point, this is the reflection on the top spot, further adjust the lift can find like this tip.
2) the sample with high surface finish (such as microhardness blocks) should use edge image finding method.
Microhardness test, sample surface roughness are generally not very high, often is a mirror, on the surface, no obvious observation characteristics, and all at high magnification in the microhardness meter measuring microscope depth of field is very small, only 1 ~ 7 microns, when focusing find like plane so, for lack of experience of the operator is very difficult, even damaged lens, Therefore, the operator sometimes retains the surface traces to find the image plane, but sometimes there is no residual trace, it is recommended to use the edge image method. That is, the center of the lighting spot (about 0.5~ -1.1mm) is aligned with the contour edge of the sample surface in the same way, and the semi-bright and semi-dark junction is seen in the mirror field of view, which is the contour edge, and then step-adjust the rise and fall can find the image of the surface edge.
(2) Adjust lighting
To prevent oblique illumination influence on the measurement accuracy of indentation diagonal long thin, to adjust the lighting light source, the indentation in the field of center according to the two points of the four diagonal area range of brightness is consistent, by observing the micrometer eyepiece in creasing like clear degree, lighting light source can be the up, down, forward, backward, left and right direction slightly move, until the observed indentation like the bright, Until there is no shadow: the differential cylinder of the moving table moves the indentation image forward, back, left and right, and the field of view of the micrometer eyepiece should be bright and the indentation image without shadow is better.
(3) Visual alignment
As we know, when measuring indentation with a measuring microscope, the indentation is magnified by an objective lens and imaged on the demarcation plate in front of the eyepiece for sighting measurement. Due to the human eye visual differences (such as normal eyes, myopia, farsightedness), as a magnifying glass effect of ocular must be put in different position, clear the scribed line of reticle to observe (immediate line at this time as the "thin"), the step (adjust the eyepiece) relative to the reticle distance is called the visibility reformed, or it will affect the accuracy of measurement.
(4) correction of indentation position
If the indentation image seen in the field of view of the micrometer eyepiece by test force is loaded with a large offset field center, the indentation position needs to be corrected. The indentation position needs to be adjusted repeatedly through several adjustment screws of the objective seat until the indentation image is centered in the field of view of the micrometer eyepiece. Do not move table when adjusting D screws) and lock each other.
(5) focus
In order to find the correct imaging position, care should be taken to adjust the indentation edge clear, not the indentation diagonal or diagonal intersection point clear. What we need to measure is the diagonal length of the pyramid on the surface of the pit. To help operator to master this step, "parallax discriminant method" is put forward here, with reticle scribed line or cross intersection point on the indentation diagonal top, moving around eye relative to the eyepiece, at this time as the focus is not correct, the indentation like edge is not completely on the reticle, will find this edge relative to the points and lines can move around. This indicates that the focusing is not correct. If the position of the eye relative to the eyepiece is inconsistent, there must be measurement error. At this time, the focus should be further focused until the edge relative marking has no relative position when the eye shakes.
Master the correct measurement method
1. Rotate the measuring eyepiece so that the movement direction of the demarcation plate is parallel to the diagonal direction of the indentation to be measured, so as to avoid the influence of the Angle between the two on the measurement accuracy. If the Angle of the two is C and the actual length is, EO will measure the length D ': D/osC, and for the intersection point of the crosshead to aim at the top of the indentation diagonal. When the two have an intersection Angle, the diagonal tip will be aligned with the intersection point of the crosshead, and the other end of the tip can not be aligned.
2, measurement of the indentation diagonal length, when aiming at the indentation diagonal must be aimed at both ends of the top, do not have to consider the indentation prism quadrilateral situation. This line is a straight line on the reticle is not a problem, for the reticle is scribed line on the reticle, targeting indentation edge or diagonal of the top debate frequently occurred, to unify various points crossed the aim, so make sure the principles, which can solve the edge varied aimed at problems under complex conditions.
3. Several problems should be paid attention to in measurement
(1) Mechanical micrometer mechanism measuring eyepiece, measurement should be unidirectional rotation micrometer handwheel, eliminate the impact of air loop on measurement..
(2) For the micrometer eyepiece of simultaneous measurement, the operator should pay attention to whether the zero of the micrometer reading is correct when the two marking lines coincide. If not, it should be normalized and simplified or corrected after measurement.
(3) for the digital micrometer eyepiece, after each boot should make the two marking board lines coincide, and then press the "reset key" to clear the reading.
(4) when the indentation of two diagonal length is not equal, the length of the two diagonal should be measured and take the average value.
(5) After rotating the measuring microscope eyepiece so that the movement direction of the demarcating plate is parallel to the indentation diagonal to be measured, the diagonal can be perpendicular to it. Move the table so that the diagonal line falls on the track of the crossing point of the demarcation board, but when aiming with this crossing point, turn the handwheel of the micrometer eyepiece and do not move the table.
(6) Operators should be trained strictly and often check their aiming accuracy with standard microhardness blocks.
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